Sam can remember when Dean and Castiel met. He'd only been four, but he can remember that intense gut feeling that Cas was Important.
So now, sitting in the kitchen with coffees and a pie that Sam brought because weekends at home should mean pie, he isn't surprised at the news.
"I'm...Cas and I..." Dean fumbles words like Sam fumbled over footballs on the junior varsity team. "We're kinda together now."
Sam can count his level of surprise on two fingers. Mostly because he's surprised either one of them made a move. "Okay."
"Okay? That's it? I spend your entire life straight--"
"You say that but I've never actually seen you have a real relationship with a woman," he points out and takes a drink of coffee. "I mean, I've seen you date, but..."
"Lisa!" is the defensive reply.
Sam scowls. "Ben hated me and that was two terrible years I try to forget."
Dean plays with his pie. "They weren't terrible, Sammy."
"So you just thought I'd love football?" He starts before cutting across any possible answer. "Whatever. I don't care about you and Cas."
He looks down, takes a bite of the pie. "Huh. 'Kay." After a pause, he adds, "Good pie."
With a sigh, Sam follows suit with the pie, savouring a bite. "I don't mean I don't care. I've kind of been waiting for it."
Dean looks up at him. "Yeah?"
"Not weirded out?"
"Only a little, because I'm crazy surprised he finally made a move," he says, chuckling.
Dean glares. "Hey, I made the first move."
Raising his eyebrows in invitation, Sam asks, "Oh yeah?"
"Trust me, kid, you don't wanna know." Dean looks down and tries to hide his smirk with a bite of pie but it doesn't really work.
"Oh, ew." Shaking his head, Sam sets down his fork, done. "Whatever, look, I'm happy for you guys but keep all details far, far away."
He gets a smile, a real and amazingly bright smile. "You're happy for us?"
"Yeah. Woulda been cool if you could've figured it out seventeen years ago. Feels like it's just been wasted time."
Cas emerges into the kitchen, eyes half lidded and searching for the coffee when he catches sight of the Winchesters at the table. "Hey, guess I fell asleep last night, huh?"
Dean looks downright nervous and Sam kind of wants to laugh. "I told him."
With a smile, Sam nods. "Welcome to the family."
While Dean coughs on his pie and mutters something about "Not getting married or anything," Sam watches as Cas gives him a rare smile. It's not big or wide but it's a twitch of lips and bright eyes. "Thank you, Sam."
"Oh," he says after a second, smile falling and eyes going wider, he walks out of the room.
"Uhm, Dad?" Sam starts, looking back at Dean in confusion. "Your boyfriend just got his 'forgot to turn off the stove' face."
Dean shoots him a look. "That happened once."
Before Sam can respond about it being when they were on the way through Kentucky for Cas' first Winchester Christmas with Grandpa John, Cas reappears and hands Sam a gift bag very seriously.
"This is from your grandfather and me."
Dean watches suspiciously. "You and dad came up with a present to give Sam for no reason?"
"Oh, there's a reason," Sam corrects with a snort, looking into the bag. He pulls the book out, showing it to Dean.
"Really, Cas?" He demands, snatching the book. "Jennifer Has Two Daddies?"
Cas' eyes shine with humour and Sam looks to see his father looking at the other man fondly. After a moment, Cas offers plainly, "We thought it would help Sam make this transition."
And if later that day they separate a little too quickly when Sam comes downstairs from a shower, it is made up for when Cas leaves to use the lav at dinner. Dean leans over seriously and offers, "And just so you know, in the spirit of friends first and all that crap you've been saying since you were sixteen..." Dean trails off and takes a deep breath, seemingly entranced.
Sam looks that way to see Cas picking his way back through tables. "Those years weren't wasted," Dean finishes in a rush before grinning when Cas looks up at him.
Rolling his eyes, Sam smiles. Dean met Castiel shortly after Sam's fourth birthday and the two of them haven't managed to surprise him once since.