I read a fic not too long ago where Sam gets possessed and Dean didn't know. Once they were back in the motel room, the demon rapes Dean and plans to kill him, but he is able to exorcise it before that happens. Once Sam is back to normal, he's horrified at what happened and they both try to figure out how to deal with it. Not a wincest story. I believe Missouri is in it, John as well. For some reason I didn't bookmark it, but I really want to read it again! If anyone knows where I can find it I'd really appreciate it!!