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They’ve always been inseparable, ever since the Winchesters got to the neighborhood and blue eyes met green for the first time. They play together and run together and nap together and fight together, even though no argument has ever lasted longer than a couple of days with them (it’s a well-kept secret, but Dean always cracks first). They learn their numbers, and Cas is there when Dean gets his first girlfriend —- there when she breaks up with him. They learn about life and friends and loss, so when Michael, Cas’ oldest brother and legal guardian, finally confirms that their dad who’s been “away on important business” ever since Dean met the Novaks is not coming back, Dean is there to stand next to a silent Cas — and then to sneak into his room that night to hold him when the tears finally come (it’s the only time Dean has ever seen Cas cry and he vowed to himself that night that he would do everything in his power to never see it again).
Cas and Sammy get along fantastically, always have, and Dean might tease them about their shared bond of nerdiness but secretly he couldn’t be happier — that two of the most important people in his life get along so great. That’s about all Dean needs to be happy (that and his mother’s pie and knowing that one day he’ll inherit the Impala — well, and he also needs his parents, of course, they’re also important, but he’s at that age where he wouldn’t be caught dead admitting to it — or any of the other stuff, really, Dean’s not like Samantha, who feels the need to go into his feelings between every inhalation and exhalation).
Considering all of this, it really shouldn’t have come as a surprise to Dean when they’re having dinner one night and John and Mary are reminiscing about the days when they first started dating — and Sam pauses in between bites of salad (seriously, what is wrong with that kid? Who refuses steak?) to ask their father, “So how did you know mom was the one?” He only pauses long enough to take a large gulp of water before continuing, “Was it like Dean and Cas?”
And for a moment the only sound that can be heard is Dean choking on his food and trying to dislodge a particularly stubborn bit of potato that seems really determined to try and go into his lung. And then his parents just share a warm look and laugh and go “Something like that.” And Dean is just staring at them because what the hell? Okay, so he hasn’t dated any girls in a while and he never brought them home, but he’s pretty sure he’s mentioned them to Sam at some point… or had he? Oh man, maybe he hadn’t and now his little brother thinks he’s dating his best friend and, god, does everyone think that?
Later, when his traitorous parents finally go to bed, he sets Sam straight and explains how Cas and him are just friends, and for some reason his little brother takes it just as well as if he’d told him their parents were getting a divorce.
When he brings it up with Cas while they’re playing video games at his house the next day (well, more like he's playing, Cas is actually reading the book they got assigned for their English class this semester, the nerd), the distress obvious in his voice, his best friend doesn't even look up from his book. Dean is a little offended.
"Dude, are you even listening to me?"
His only answer is a vague “mmhmm”, and now Dean is just pissed.
"Cas, dude. Sam thought we were dating. Dating!”
The response is, as expected of Cas, not quick to come, but when it does, Castiel’s tone is just as calm and even as if they were discussing the weather.
"I fail to see why you would be so surprised. I would not be opposed to being romantically involved with you."
And. Well. Dean’s too young to almost choke to death twice in less than 24 hours, but that doesn’t seem to stop his body from trying.
He doesn’t manage to come up with a response on the spot and Cas goes back to his reading as if he hadn’t just basically confessed he likes Dean. So Dean just sits back down and goes back to playing his video game and tells himself not to think about this again, because, Jesus, he was turning into a girl, and if Cas didn’t think this was a big deal, well, he wouldn’t even waste the brain power thinking about it.
So of course it’s the only thing he can think about for the rest of the week (and man, how that messes with his sleep).
After 8 days of barely getting any sleep, Dean is irritable and short tempered, so when he shows up at Cas’ doorstep, arms crossed and a frown on his face, his “Fine. Let’s try this. Kiss me.” sounds less like an invitation and more like an angry command.
Castiel doesn’t seem to mind. He closes the door quietly behind him and steps forward, tilting his head a bit to the side in that way he does when considering a particularly interesting specimen in Biology class. Dean’s not too happy with the comparison, but he soldiers on.
"Kiss you?"
"Yes. Let’s test this stupid theory of Sammy’s so I can stop thinking about it."
He figures it’ll be totally awkward and like kissing his own brother — oh god, the mental images, he never wants to think about that again—, and then he can go up to Sam and explain that they’d tried it but it’d felt wrong and that they’d both agreed they worked better as friends — and he’ll have Cas on his side this time, who’ll explain to Sammy in his logical ‘I’m going to be a professor one day’ voice and then his brother will stop looking at him like Dean ran over a puppy and then stopped to laugh at its misfortune.
Castiel stares at him for a moment (long enough for Dean to start questioning the soundness of his plan), then cocks his head in the other direction, gives a small awkward shrug and says, “Okay.”
Dean doesn’t even have time to freak out, because then Cas kisses him.
And crap.
There’s no way Dean’s going anywhere near Sam now. He doesn’t want to get told “I told you so”.
He only pulls back enough to grumble a resigned ‘Fuck’ before he’s pulling Cas closer again.
Damn it. He hates when people get things before he does. Especially his baby brother.
He’s gonna have to add food dye to his shampoo again.
Fuck.