Work Text:
The drizzle was more than fitting for a shitty day like today. It was just short of real rain, too light to commit but still clinging annoyingly to hair, clothes and patches of bare skin, coating London’s streets with a wet sheen that reflected the city’s lights in a distorted way that hurt Sirius’ eyes.
Not like it was hard, these days - not with the war sitting in the back of their necks and always being in the forefront of their minds, its looming threat following everyone like a second shadow. Some were just more aware of it than others. Some feared it more than others. Really depended on whether you had a name for the danger lurking around the next corner, or understood what to attribute your losses to. Or your regrets.
Or both.
That’s the reason why Sirius Black had chosen London for tonight's occasion. The city had enough people who understood their current reality well enough to be wary, even if they didn't understand the full extent of the Wizarding War, but nevertheless the city still held its promise of anonymity and false peace due to its sheer size and the masses of disinterested Muggles who lived here, interacting with each other as strangers on a daily basis under the pretense of normality.
Nobody looked twice at the black-haired stranger who had his shoulders drawn to his ears and held his head down to stop the drizzle from getting in his eyes and blurring his vision. Nobody cared that he didn’t carry an umbrella or that he walked through the streets unreasonably slowly considering the bad weather. If anybody looked at him, then it was only because they had a passing appreciation for his black leather jacket, for the wet curls framing a handsome face, or the chain accessories that hung from his trouser pockets and rattled softly with each long step he took.
Sirius Black had a rough idea of where he was going: simply follow his nose, see which place would catch his attention and where he would waste away the night, alone. Usually, he might have had a real plan. The Marauders usually had had plans for their pranks, during their prime time at school. But more often than not, the four of them had just followed their gut and well, Sirius was still a Marauder through and through. The war hadn’t changed that, at least.
“Nice excuse, Snuffles. Just admit you're a bad boy who never cared much about your responsibilities in the first place. Being a Marauder was just a bonus,” James’ phantom voice quipped at the back of his mind, making Sirius grin fleetingly.
His responsibilities. Yeah, he never much cared about them when he should have.
Automatically, Sirius looked up at the sky, ignoring that the rain was now free to drum its cold, spindly fingers against his cheeks and eyebrows, chilling him as it ran down his face in thin, wet trails. Sirius’ eyes scanned the sky for the familiar constellations, despite the heavy clouds blocking his view, but every Black knew where their stars were in the night sky, even if they couldn’t see them.
That’s when Sirius spotted the bar’s name: “Happiness Forgets”. Wouldn’t he like that to be true. Though Sirius guessed that was as good a reason to drink as any - the futile pursuit of happiness, mixed with the desire to forget.
Stopping, Sirius buried his hands in his trouser pockets and continued to look up at the inconspicuous sign that had somehow caught his eye, its curved chalk writing on a simple black board, an invitation above an equally inconspicuous staircase leading down, the sign without any neon or fairy lights to advertise for customers. Easy to overlook. Not many people hanging around. A place hidden underground, probably without windows.
Just what Sirius had been looking for.
When he entered a few seconds later, he suppressed his first instinct to shake off the raindrops like a dog and headed straight for the bar at the other end of the room, behind which rows and rows of blessed bottles stood on display, waiting to be bought and tasted.
“Give me the strongest you have. Whatever that is.” Sirius sat down on the nearest bar stool with a cursory glance around the place, more out of a habit drilled into him after months of expecting threats from every corner than any real interest in the bar’s interiors.
His mind immediately dismissed the unimportant details he noticed: groups of friends at other tables enjoying a drink together; the rather homely lighting that tried to drown out the shadows without being obtrusive, but ultimately failed at both; the vaguely familiar popular music that invited people to dance.
Thankfully, Sirius didn’t feel a drop of magic in the air, just ordinary life and sounds, so he allowed himself to turn to the barman across from him behind the bar counter and scrutinise him next. Normally, Sirius would first sense if something was off with his subconscious; his dog senses were much sharper and faster on the pickup than his human instinct or perception. But looking at the nondescript barman, there was no faint tingling somewhere behind Sirius’ eyes that would be enough warning for him to act.
Meanwhile, the barman continued to stare into Sirius’ face, not reacting to Sirius’ words. Had his eyes not been a pale, watery blue like Wormtail’s, the barman’s attention could’ve been described as “intense” as he stared at Sirius without a word, barely blinking. Something about Sirius seemed to put the man on his guard. Maybe he was looking at Sirius and all he saw was trouble for his bar, because to be fair, Sirius’ appearance spelled trouble from head to toe and being drenched didn't help. Perhaps the barman was weighing his options, considering whether to serve this customer or kindly ask him to leave.
That's what Sirius imagined as he looked back at the barman, pretending not to be bothered by the situation.
“No preferences?” the barman eventually asked, and at the underlying stiffness in his words, Sirius finally relaxed.
Ah, Sirius thought, allowing his lips to curl in the ghost of a smile. He had been pigeonholed, put into a cosy box of made-up expectations. All the better, because when people had certain stereotypes for you, all you had to do was fit in and meet their expectations to fly under the radar.
“I’m just looking to get drunk. Absolutely hammered,” Sirius explained, smoothly. “I want to wake up with a splitting headache tomorrow morning and not remember a second of tonight, so whatever you think will do the trick the fastest will do.”
The barman still didn’t move an inch, his watery blue eyes transfixed on Sirius’ face. He was obviously not convinced by something, hesitating to give Sirius what he craved for.
“If you’re worried about money, I can pay.” Sirius reached into the right pocket of his jacket and dropped a handful of coins on the bar between him and the barman. “And believe me when I say that I’m older than I’d like to be, but you can still check my ID if you insist.”
“No. That uh … that won’t be necessary. Thank you.” The barman shook his head and absentmindedly raised a hand to run it through his hair, but when his fingers brushed over his military cut, slightly off the mark, he seemed to be taken aback by his short hair and immediately dropped his hand again. Judging by this unconscious gesture, the barman must be used to having longer hair, maybe about as long as Sirius’ was now. He must’ve cut it recently, and old habits die hard.
Sirius briefly imagined what it would be like, to radically cut off his wavy hair and give up the curtain that framed his face and could either be his fashion statement or a shield from the world.
Hm, no - Sirius didn’t want to imagine it. It was like asking him to leave his jacket behind, or part with his beloved motorcycle. And Sirius had already suffered enough losses in his life.
“Bad weather outside. Here.” When Sirius refocused on the present, blinking repeatedly, he noticed that the barman was holding out a small white towel to him, waiting for Sirius to take it. Sirius raised his eyes higher, wondering since when this had become part of the service in a bar, and thought he saw reproach in those pale, blue eyes. What, like the weather was Sirius' fault?
“For your face,” the barman said impatiently, giving the towel in his hands a little shake. And yep, Sirius had not imagined the silent accusation in the barman’s gaze - just now it was bleeding into the rest of his face, wrinkling his nose and thinning his lips in that haughty way that Sirius knew from his worst nightmares and hoped to never ever catch himself doing in the mirror -
Like a Black.
But Sirius would know if he was related to this barman, surely. Like, what were the odds that this dark blond Muggle, who was neither lanky nor fit nor particularly tall or handsome nor seemed to recognise him, was secretly a Black?
Right. Zero.
“What’s your name, if you don’t mind me asking?” Sirius asked, just to make absolutely sure. And just so nobody got the wrong idea, he added as he took the offered towel and used it to wipe the water from his cheeks: “So I know who to properly address my verbally expressed thanks to.”
Prongs and Moony would've been proud of such eloquence. Or would've made fun of Sirius. One of the two.
“John.” The barman picked up a glass he'd mixed, filled with an ombre drink that went from black at the bottom to dark green liquid and a sugared rim at the top, and placed it in front of Sirius with a gentle clink. Staring at it with mixed feelings, Sirius decided that these colours, which were distinctly Slytherin, were actually perfect for tonight’s occasion ... as if the barman had known what Sirius was here to celebrate. “John Oliver Doe, if you need to know.”
Sirius snorted, and, realising what he had done, quickly turned the snort into a cough, trying to hide it in the now damp towel. Somehow he could tell that the barman knew anyway, though John's expression was carefully neutral as he took the towel back and turned away to tuck it away somewhere under the sink.
“Well. Thank you for the towel, John Doe,” Sirius said, trying his best to sound sincere, even though the name cracked him up for some reason, as if nobody should ever be called ‘John Doe’. In the back of his mind, Sirius could practically hear Moony asking dryly if someone called Sirius Orion Black should find this funny in any way.
Sirius shushed Remus’ voice, closed his fingers around his glass, and raised it before he could think about it any more. He had come to this bar for one reason: to drink and to regret on this very special day, and he intended to do both through the night and well into the morning. What he had told the barman earlier hadn’t been a lie.
“To a fuckton of regrets. Cheers.”
Determined, Sirius threw his head back and downed the Slytherin-coloured liquid in one go. It did burn like his regrets all the way down his throat and almost made Sirius gag at the awful taste, but as soon as it hit his stomach like a well-aimed punch and settled, the alcohol kicked in and began to prickle pleasantly like strong alcohol tended to do, dulling his senses enough to make Sirius relax a bit more.
Sirius carefully put down his glass and pressed his palms flat on the bar in front of him, taking a moment to regain his bearings. He had to take a couple of controlled breaths until his head stopped swimming. Whatever this alcohol mix was, it really did the trick.
“Regrets? You?” the barman - John, Sirius reminded himself - asked it in a tone that Sirius couldn’t quite place but which made him arch an eyebrow in silent question. John had narrowed his eyes, studying Sirius quizzically, his chin slightly raised in a way that struck Sirius as vaguely familiar. “Relationship regrets?”
Ah, there it was again. The stereotypes Sirius had been pigeonholed into. … Or was it?
Relationship regrets.
Absentmindedly gesturing to John for a refill, Sirius thought about this question some more, fully aware that the burning in his throat wasn’t just because of the alcohol anymore, now that he devoted his thoughts to the question in earnest. John wasn't too far off the mark. Sirius had many regrets when it came to relationships.
The Prank, of course, right up there on the list of Sirius’ biggest regrets.
The Marauders going their separate ways after school, a more recent one that Sirius blamed on the war but knew was more complicated than that.
Regulus’ death.
“… in a sense,” Sirius said after a while, soberly. Let the barman believe that Sirius was talking about past partners that he regretted, or whatever John had in mind when he asked about Sirius’ relationships. Though the way the question had been asked had sounded judgemental to Sirius’ ears, as if John didn’t think Sirius could ever regret anything - surely, however, that was all in Sirius’ imagination.
The barman and he, they didn’t know each other.
Picking up his second glass of alcohol, Sirius raised his hand in a toast, directed at John, and said as solemnly as he could, in the spirit of today's occasion: “To my brother Regulus.”
Even as Sirius brought the glass to his lips and downed the drink in one go again, he noticed from the corner of his eye how John stiffened. A normal observer would’ve missed it, not having paid attention to miniscule shifts in body language, but Sirius hadn’t been a normal observer since he was old enough to suffer Walburga Black’s parenting, which had made watching people and not missing cues a critical question of survival.
This time, Sirius lowered his glass slowly, not taking his eyes off the barman, who had lowered his head and seemed to be forcing himself to move his hands in an attempt to appear casual. It was just to keep his hands busy, Sirius recognised the nervous habit - Moony did it with books or with dishes or whatever was closest when he was nervous, and James did the same with his glasses or his tie or just played with his fingers, thinking Sirius wouldn’t notice.
Regulus had always done it less obviously, holding on to the strap of his bag to hide the fact that he was flexing his fingers, or playing with his cloak when his hands were joined behind his back, always trying to hide it from plain sight. The only times Regulus hadn’t done this were during Potions, with glass phials, scales and whatever potion ingredients were around, because Regulus always lowered his guard around things he liked.
Before he died, anyway.
“Your first toast was to your regrets.” John must have felt Sirius’ eyes, because he began to speak unprompted, his attention entirely on his hands as he took another glass and began to mix another drink, a different one from the one he’d made for Sirius.
Watching John's hand movements was calming for some reason, familiar. This time, Sirius tried to hold on to the thought, sure that he hadn't imagined John's suspicious reaction to the toast, but Sirius couldn't focus on his suspicions and John's question at the same time. “You followed up with a toast to your brother. … Is he … Is he one of your regrets?”
Frowning, Sirius pushed his empty glass across the bar towards John and leaned forward to slump over the tabletop, one hand buried in his hair, the side of his face pressed flush against the length of his forearm. He felt at war with his head just two drinks into the night and although he had admittedly wanted this, a more conscious part of him understood that something was off.
And Sirius was already too drunk to focus on picking apart what exactly it was. A fact which, admittedly, should worry him more than it did at the moment.
“I'm toasting because it’s my brother’s birthday today,” Sirius said. A frown had settled between his eyebrows, something between an attempt at concentration and genuine annoyance, which only grew at John's curt reply.
“This doesn’t answer my question.”
“Really, are you this nosy with all your customers, or do I get the special treatment?” Even through the haze of alcohol, Sirius knew that his tone was sharply hostile, but when he tried to smooth over it with a toothy smile, the result was just as sharp. Yet when John glanced up at him, the barman just huffed an unimpressed laugh, obviously not bothered by Sirius' attitude.
It was almost as if John knew Sirius was going to react like this. And even in his state, Sirius understood that this was impossible, unless …
“Here you go. On the house.” John had picked a straw to put in the freshly mixed drink and pushed it across the table before lowering his upper body to lean on his elbows and looking up to meet Sirius’ wary gaze head-on. “To disappointing brothers.”
Do I know you? Sirius wanted to ask but was distracted by the undisguised challenge in the barman’s eyes.
Oh.
“He wasn’t disappointing,” Sirius contradicted John, taking care to enunciate to bring his message across very clearly, and shook his head slightly to clear his mind. It still lagged a second behind what his mouth was telling the man on the other side of the counter. “Regulus was the brightest in his year, and the teachers loved him. His problem was his bloody pride. He refused to listen to me, stubborn mule that he was, always insisting that he didn’t need my help.”
But you already know that, don't you? Sirius thought.
He couldn't find any evidence of that in John's face. If anything, John just looked mildly curious. Was Sirius being delusional, blinded by grief, regret and a good part of toxins in his system?
“You talk about him in the past tense.”
“Yeah.” Sirius agreed although it wasn’t phrased as a question, and averting his eyes, took a sip of his new drink, barely noticing how much sweeter it tasted. “He killed himself last year. Saw a small notice about it in the paper, and that’s it. I kinda wish he’d left a note or something. Anything.”
“Do you hate him for it?”
Sirius snorted. “There are a lot of things I hate Regulus for. But trying to do the right thing and resist … that’s the most courageous thing he could’ve done. Or maybe that was just the coward in him, chickening out when he should’ve committed to it like he had always wanted to. Either way, I’m proud of him. And pissed off that he got himself killed.”
I wish I had been there to help him when I had the chance. Get him out of that house too. Get him to open up. Give up his pride. - All these things Sirius left unsaid. They’re regrets he’d carry with him all his life, his personal burden.
Sirius shrugged and laughed bitterly. “Doesn’t matter much now, does it?”
For all the perfect boy Regulus Black had been, he had still followed in Sirius' footsteps and ended up turning his family against him. And in fact, Sirius was still too sober for all that sentimental shit.
Letting his head hang, Sirius brushed his thumb across the condensed surface of his glass, which was still mostly full. Then he raised his glass for the third time that night.
“I’d rather raise a toast to the boy my brother was before I abandoned him and left him alone in that bloody house. Before it poisoned him. Happy birthday, Regulus.”
By the time he had finished his third glass, Sirius hardly remembered things clearly anymore, mostly impressions coated in the warmth of alcohol. Sirius remembered planting his face against the table's wood so that the world around him would stop swaying. He remembered feeling sick and John handing him a small glass of clear liquid (water?) that stopped him from spilling the contents of his stomach all over the floor. He vaguely remembered crying at some point.
And talking, opening up to a complete stranger after only three glasses, pouring out truths like a waterfall that he'd never say in the light of day.
“James - the apple of my eye. James said … he said that his saviour complex must rub off … on me. Prick. But I know I could’ve done it. Yes. Get Regulus out of there, I mean. I did it, John. I got out of there.”
“I know,” John said, shushing Sirius and patting his shoulder rather awkwardly. It should’ve sounded like a throwaway comment from a random barman in a random bar to calm a drunk person, but John said it too sadly, as if he really did know. As if he understood what Sirius was saying.
“All I do is make mistakes, mistakes, mistakes, all my life,” Sirius confessed to him, whining and clinging to John's arm as they swayed across the room towards the stairs that would lead out of the bar. He stumbled over his thoughts in that state between understanding the world and not understanding a single damn thing, especially himself - a third eye that was blind. “And then I regret and then I drink, to forget. My toast to ... to Regulus, it’s just as pretentious as the rest of them, but - but I can’t do anything about the Black blood in my veins. Being pretentious is part of who I am.”
Sirius wasn’t sure if he was saying all these things at all or if it was all in his head.
I’ve made so many mistakes. Things I’m not proud of. I should’ve tried harder to get him out because I knew there was one. A way out. I was the older brother. I was supposed to care. I was the only one who knew who Reg really was. I knew what mother was like. What it would be like for Reg. I should’ve …
“You were a child,” John said, leaning Sirius against the nearest wall with some effort, a firm hand on Sirius' shoulder to keep him standing. Somehow they had made it out, up the stairs and into the fresh air and Sirius was able to breathe again. He inhaled the fresh night air greedily and felt his head clear a little.
Only then did he register what John had said.
“What?” Sirius asked thickly and looked bleary-eyed at the man who was still supporting him, helping him to stay upright. In the streetlights, John’s hair looked much darker than it had in the bar, almost dark brown. Longer. And his eyes …
“Stop acting entitled, that’s what. You were a child.” John averted his head, his jaw working. “You’ve made mistakes. Everyone does,” he said.
Sirius gaped at him. He was too drunk for this conversation, but he felt like this was important. It seemed so important.
“I was sixteen,” Sirius said, pressed his eyes shut and the heel of his hand against his brow, trying to focus. He had been sixteen when he left that damned house, but before that, throughout his childhood, there had been ample opportunity to mend the gaping rift between him and his brother - to change their future. To reach out.
Somewhere, in another universe, the Black brothers would’ve stuck together through thick and thin, drinking to Regulus’ birthday together, making jokes about his age even though Sirius was the older one, and getting hopelessly drunk until they stumbled home through the twilight streets - together.
But this wasn’t it.
This was just John and him.
“I was sixteen,” Sirius repeated, his head sagging onto his chest for a second before he caught himself. Irrationally, he thought he heard John answer him in Regulus’ voice, his tone as accusing: “You don’t have the power to move the world. Not everything revolves around you all the time.”
But it was impossible, because Regulus was dead.
“You …” Sirius forced his eyes back open to stare at John, but the barman had taken hold of Sirius’ raised hand and slung Sirius’ arm around his shoulders, dragging him further down the street, the two of them stumbling along.
Sirius thought he was going insane if he had started hearing his dead brother’s voice. He desperately needed to lie down and sleep.
“Where to?” John asked, adding more suspiciously: “You do have a place to stay tonight, right?”
“Mh? … Here. Here is ... good.” To be honest, Sirius just wanted to curl up somewhere as Padfoot and sleep until he was sober enough again to Apparate somewhere else, but those persistent hands held him upright, insisting that he walk and focus on the conversation, even though Sirius didn't want to.
His head hurt.
“It’s not safe here. Do you … or can you … no, in this state you can't even walk straight.” John groaned in exasperation. His fingers curled into Sirius’ leather jacket, making Sirius wince. “I thought you were supposed to be the responsible one, but look at the state you’re in! Do you at least have your wand with you?”
“Hah?” Wand? Had John just mentioned wands? Why did the Muggle barman know about wands? Hm, no, he must’ve said ‘phone’ because Muggles ask about phones when they want to see if someone can pick up their drunk friend, Sirius remembered from Muggle Studies.
Yes. Yes, phone.
“Oh bloody hell, never mind! Come on, my flat’s not far from here, we’ll make it just in time. Just hold on to me, Sirius, will you? We’re almost there. We can take the elevator inside.”
Sirius. Had he told John his name? Sirius couldn’t remember if he had told John his name. He must’ve, and it had simply slipped his mind, but in the drowsy haze of the alcohol he couldn’t remember anyway.
Everything was a mess, especially Sirius’ mind.
He must have blacked out again because the next thing he knew, he jerked awake at the distinct sensation of magic around him, although the sensation itself had only lasted for a second, the time it took for an entrance door to open and close.
Wards. The flat was warded by magic.
Powered by a surge of alarm and adrenaline, Sirius automatically reached for his wand, even though in his state, he couldn't tell if the magic had been hostile. But he couldn’t find his wand, and panic flooded his sensesm shortening his breaths and making his head spin. Where was his wand?
Sirius lost his balance and fell onto a couch, caught by slender hands around his shoulders. The unmistakable voice - no, the annoyed tone of voice made him freeze.
“Drop it, Sirius. I’ve got your wand.”
Sirius threw his head back so hard his neck cracked, meeting familiar grey eyes framed by wild black hair similar to Sirius’, the face still handsome but much paler than Sirius remembered, the cheeks more hollow than they used to be. Sirius’ lips opened with a name that threatened to choke him - but it couldn’t be.
He was dead. Has been dead for more than a year. Sirius had grieved for him.
Regulus let go of Sirius' shoulders when he was sure that all the fight had left his brother, and smoothed out his expression into that empty Black look that both brothers carried around like a mask - a family heirloom, in a way.
“Rest here. Sleep. This place is safe.” Regulus turned away and began to peel off clothes - John's clothes - that hung too large from him, disappearing into an adjoining room.
No, wait, Sirius wanted to say, unable to speak, his heart racing like a scared rabbit’s. Stay. Can it really be you?
Sirius heard him change in the other room, heard the clinking of glass, watched him emerge again, this time in Muggle clothes that fit him. He looked thinner, marked by the war like the rest of them, but still moved with the proper Black manners that had been drilled into him since childhood.
There was no mistaking him.
“Regulus?” Sirius croaked, and Regulus regarded him with a tense smile. He stopped several steps away from Sirius, hovering uncertainly in front of the sofa, his fingers flexing around the small phial in his hands.
“Here’s an Invigoration Draught against the headache you'll have in the morning. In case you change your plans,” Regulus told him, took a small step forward to place the phial containing a clear blue potion on a small table next to the sofa and stepped back immediately.
They stared at each other, both faces blank, neither saying anything. Regulus was the first to break away. Under Sirius’ watchful eyes, he disappeared into the other room and returned with Sirius’ wand in his hands, gingerly placing it next to the phial of Invigoration Draught before reestablishing the distance between them.
“Your wand," he said unnecessarily. "I sent a Patronus to Potter to let him know that you’re all right.”
“You can summon a Patronus?”
“On good days, yes.”
“Where’s your wand?” Sirius thought he might be in shock on top of the alcohol. His head was empty, severely lagging behind reality. He put his elbows on his knees and buried his head in his hands, staring blankly at the floor. He could still see the toes of Regulus’ shoes in his field of vision.
There were so many things he wanted to say to his brother. He didn’t say a single thing.
“You should sleep,” Regulus said, and the shoes moved.
“Stay,” Sirius said, his head snapping up, the panic flaring up again. He couldn’t lose Regulus again, not when he had just found him. Not this soon. “Please.”
“The wards will keep you safe tonight. Your friends know where you are.”
“Regulus -”
“No.” Regulus interrupted him curtly and turned his head away, his jaw working again. Now that the face of John Oliver Doe had melted away, Sirius understood what a fool he had been not to have recognised Regulus’ tells immediately. They had always been there, hidden in plain sight - the way Regulus held himself, the way he handpicked his words and talked with his eyebrows and the corners of his mouth, the stiffness of his shoulders.
If Sirius hadn't been so blind, he would've seen the truth sooner.
“Please,” Sirius repeated pleadingly, his voice thin, frightened and weak.
Regulus exhaled all his breath through his mouth, then crossed the room and sat down stiffly next to Sirius, eyes determinedly fixed straight ahead, hands clenched into a fist between his knees.
“Promise you won’t go looking for me,” Regulus said through his teeth.
Sirius studied the familiar profile, the aristocratic nose, the stubborn line of Regulus’ lips, a face that was handsome in the way that works of art made from stone, carefully carved and shaped into form, were. And yet Sirius discovered new scars on his little brother, not all of them visible on the surface.
“They said you were dead. You’re not.”
“Promise it, Sirius.”
“Do you want them to continue to believe that?” Months ago, before the Marauders were thrown into the middle of the war, Sirius would’ve insisted that their side, Dumbledore’s side, could protect Regulus if only he joined them - that there was no need to be afraid and live in hiding. Now, he wasn’t so sure anymore.
Sirius let his heavy head fall against Regulus’ shoulder, feeling him stiffen at the physical contact, and said, tired: “I’ve made so many mistakes, Reggie.”
“I know.” At least Regulus didn’t shake him off but let Sirius rest his eyes, listening to Sirius’ breathing even out. Regulus waited patiently until he was absolutely sure that Sirius was asleep before he moved a muscle.
Regulus couldn’t stay. In order to ensure that Sirius would be safe tonight, Regulus had allowed the effects of the Polyjuice Potion to wear off outside his flat, revealing his true appearance to the public when he was supposed to have died in an underground cave after his act of resistance against the Dark Lord.
In just one night, Regulus had given up everything he had built up - once again. But this, Regulus could add to the list of things he did not regret one bit.
Looking down at his brother thoughtfully, Regulus reached for Sirius’ wand, pointed it at the adjoining room and said: “Accio blanket.”
Regulus caught the blanket that came flying in from the other room and gently wrapped it around Sirius, making sure it covered him. He had already performed a drying spell on Sirius’ clothes earlier, on the way to the flat, so that the dumbass wouldn’t catch a cold, or touch Regulus with cold, wet hands and accidentally trigger an episode, but this would ensure that Sirius wouldn't be cold.
Then, Regulus rummaged around the flat in search for a pen and paper and wrote a short note which he tucked under the potion for Sirius to find in the morning, replacing Sirius' wand next to it. Knowing his brother, Regulus knew that his words would fall on deaf ears, but he would be damned if he didn’t at least try to dissuade Sirius from doing what Sirius wanted.
"But trying to do the right thing and resist … that’s the most courageous thing he could’ve done. Or maybe that was just the coward in him, chickening out when he should’ve committed to it like he had always wanted to."
Emotion clawing at the back of his throat, Regulus allowed himself to linger and watch his brother for a second longer, memorising Sirius' sleeping face with the wonder and affection of a younger brother who still looked up to the older.
At last, Regulus Black removed another phial of Polyjuice Potion from his clothing, the liquid having assumed a pale Gryffindor-red colour.
With one last look at his sleeping brother and an unspoken "goodbye", Regulus stepped out of the flat, drank the potion in one go, and Disapparated with a crack.
“Sirius,
You wanted a note, so here you are. By the time you read this, I will have left London for another safe place. The Dark Lord’s eyes are everywhere. Don’t go looking for me. Stay safe.
P.S. Ask Lupin or Potter about John Doe. I’m disappointed you didn’t know.”