You've known Sam for years. When you were in middle school, the two of you became friends, and you just kind of clicked. You've liked him since highschool, and while happy for him, you were jealous of Jessica.

You, being a hunter too, heard what happened to her, and felt bad for him. When him and Dean started going on cases, you tagged along. You and Sam grew close again, and considering you went with them all the time, you got together. And while it's not technically on legal document, you're 'married'. This, of course, leads to endless teasing from Dean...

Sam, now, is sitting at a table in the motel room, doing research on a case you three are following.