It came out of nowhere, but Sam had been expecting it any day. It wasn’t one of those “we need to talk” kind of things, all “let’s go somewhere private so I don’t have anxiety over this” like a lot of similar conversations were, but it was still serious. Sam was far more mature than his brother, and he knew when not to laugh.
Dean just walked in the room and sat down across from him before staring at the table for a very long moment. Eventually, Sam cleared his throat expectantly. Dean brought his head up in one swift movement and connected his eyes to his brother’s.
“I’m bisexual,” he said plainly. There was silence.
Then Sam grinned at him. “Dude. I fuckin’ know.” Dean gave him a look of confusion and discernment and he huffed a laugh. “I’ve known since you were like, 20. It’s kinda obvious. And besides, like three weeks ago you borrowed my laptop and you forgot to clear your search history – again – and I found shit like ‘how to know if you’re bi’ and ‘how to come out to your brother’.”
Dean was silent for a second, then opened his mouth again as if to say something. Sam held up a finger to cut him off. “And now you’re about to tell me you’re in love with Cas. Knew that too. Hell, about the only person who doesn’t know is the man… angel… himself! The thing that would surprise me the most would be if the two of you were together, cause that would mean you’d actually talked to someone about your feelings.”
Dean smirked slowly. “Well, Sammy…”
“No.” Sam almost flew out of his seat. “No fucking way.”
Dean’s smirk morphed into a genuine smile. “I asked Cas to marry me yesterday.”
Three rooms away, there came a shout. “I SAID YES!” Cas’ voice floated down the hall to them.
After that, Sam wasn’t conscious of anything besides his brother’s voice.
“Stop screaming. Sammy, stop screaming. Sam! Dammit, Sam, you’re gonna fuck up your vocal cords. Sammy! Earth to Sam!”
 Think 6x19, right after Cas says, “I was never in… your…” Dean makes that face.