Work Text:
It had been a long time coming.
Magnus had been thinking about it for years, going over every consequence in his head until he couldn't think at all anymore, and he had finally decided. Alexander Gideon Lightwood was the love of his life, his future, his everything, and he didn't want or need anything else. He was tired of losing everyone he loved over and over again, living in a vicious cycle that he never had a reason to escape until then. He knew deep down that he had been waiting for a love like what he had with Alec, something so sweet and honest and beautiful, and now that he had it, he wanted to keep it.
So he had decided to give up his immortality.
It wasn't an option that many warlocks had, simply because they had no idea that the spell even existed. It had been created only just over 100 years ago, and was kept a secret from most for fear that it would be put into the wrong hands. There was plenty of evil in the world, and the last thing Warlocks needed was someone like Valentine having a spell like that at his disposal. Magnus had come upon it in his endless search for a solution to his dilemma. Alec was fine with him being immortal, and had absolutely no idea that Magnus was even considering giving that part of himself away, but the thing was, Magnus didn't need it anymore.
He used to think that it made him who he was, but that wasn't true. His immortality didn't define him. He defined himself. For once he was going to live on his own terms, not ones set by the Clave or the Shadow World in general. However, he did have to tell Alec before he did it. As much as he was sure of how much Alec loved him, he didn't want to back him into a corner and make him feel like he was stuck with Magnus for the rest of his life. It wouldn't be fair to spring that on him.
He brought it up when they were laying in bed one night, both of them far too wired to fall asleep just yet. They had a long day discussing things with the rest of the Downworld council, and when they had gotten home they decided they were tired of taking their work back with them. Instead they told each other stories, ones that maybe they'd already told, but were still just as meaningful. It had been, for lack of a better word, magical. Magnus never thought he would be able to open up like that to someone, to bear his heart and soul and instead of watching the person he loved crush them in his hands, he got to watch him hold them in his own chest for safekeeping. It brought warmth to him every time he thought about it, and he knew that moment was the right time to broach the subject.
"If there was a way for me to grow old with you, would you want that?" Magnus asked, his voice as quiet and soft as he could make it. He had his head pillowed on Alec's chest, and practically felt his boyfriend's heart jump as he froze for a few seconds.
"Is this a hypothetical question?" Alec asked, his voice somewhat strained. Magnus couldn't tell what Alec was feeling just by listening to his voice, so he shifted off of Alec, leaning his head against his pillow instead. Alec watched his every move, his eyes somewhat wide as he waited. He looked vaguely scared, but mostly shocked, which was to be expected.
"I asked you first," Magnus said simply, offering him a small smile, and Alec narrowed his eyes briefly before smiling back.
"Of course I would want that. I'll always want you." Magnus' smile widened, and he felt like he could cry. He had no idea how he had managed to find someone who was willing to stay. Alec had found a closed off, broken man, and he had figured out how to open the locked door between them in a matter of minutes. A wide, toothy smile and a seemingly endless trip over words had been Magnus' undoing in the best way possible. When he didn't say anything for a few moments, Alec urged him on, saying, "Your turn." Magnus took a deep breath, and told Alec everything.
"I've been looking into this for a long time, measuring all of my options, and I came across a spell. It can get rid of my immortality without killing me. It basically reaches back to the day I stopped aging and...cuts the string, if you will. I'll still have my memories and my magic. The only thing that will change is that I'll start getting older, just like any other mortal."
Alec was silent for a while, staring at the ceiling as he thought. His expression was unreadable, and nerves gnawed at Magnus' stomach as he waited for him to say something, anything. He would understand if Alec didn't want him for the rest of his life. It wouldn't be the first time it had happened to him, but it would destroy him completely. He had never fallen so hard, so completely, so beautifully in all of the centuries he had been alive. Alec was it for him, even if the feeling was not reciprocated.
"I don't want you to give up your life for me," Alec whispered finally, breaking the silence. He sounded sad, and Magnus' heart clenched as he sat up, grabbing one of Alec's hands between both of his. Alec sat up as well, meeting his eyes, and a lump formed in Magnus' throat. "I've always known that I'm temporary, and that's okay with me. I want you to be happy." Magnus shook his head, pushing back the tears that threatened to well up in his eyes.
"Alexander, you are my life. You are my happiness. The way I love you...nothing will ever come close if I'm left behind without you. Maybe I would be able to move on, and maybe I would find someone to love, but they would never be able to live up to what you've given me in only the few years we've been together so far. This isn't just for you. It's for me, too. I don't want to lose anyone else if I can help it. You are what I want, and I understand if you don't feel the same, but I-"
Alec kissed him, their lips crashing together desperately, and Magnus' mind went blank as he leaned into it. Every touch between the two sent sparks through his veins, heating up his blood until he was boiling inside. The slow slide of their mouths, the swipe of Alec's tongue, the lingering touches on arms and shoulders and backs and necks, was enough to drive Magnus mad, and he loved every second of it. Losing that would be like cutting out all of his vital organs all at once, and when they pulled back, their foreheads resting together as they caught their breath, Magnus knew the choice was made.
"You're sure you want this?" Magnus asked. Alec let out a slightly breathless laugh, and leaned back, nodding his head.
"Magnus, there is no other world, alternate dimension, or universe where I will not want to keep you for the rest of my life. I love you."
"I love you, too," Magnus said, finally letting the tears that had been collecting behind his eyes loose.
----
Many years later, when both of them had their fair share of gray hairs, Alec whispered as they were sitting on the couch, watching a movie. Max and Rafe had fallen asleep a while ago, and he didn't want to disturb them.
"Do you ever regret it?" he asked, and somehow Magnus knew exactly what he was talking about. He smiled, shaking his head and leaning farther onto Alec.
"Never."