I'm looking for a specific fic. From what I remember... Dean is crazy (schizophrenia, I think) and lives in some sort of mental institution, but Sam visits him and Dean is his best friend. I think it starts when Sam is much younger and is told from Sam's POV. It's a non-supernatural AU, except that Dean believes all the supernatural stuff happened. I think Sam stays in Kansas instead of going to Stanford so he can be near Dean. Sometimes Dean thinks they're in a relationship, but there isn't really any wincest from what I remember. Dean disappears and Sam searches and searches for him and eventually Jimmy Novak calls and tells Sam that Dean is there and thinks he's an angel. It was really good and I would love to reread it!

FOUND! Link in the comments!