The fic I'm about to rec is not exactly what you are looking for but it does have Dean staying with the fae. However, it's post-Stanford.

There's No Such Thing As Faeries by thedarklordsatan
Sam is sick, and Dean can't help him. Magic won't work, and no demon will make a deal to save one of the notorious Winchesters. Just when Dean's lost all hope, his faerie godfather Castiel appears with a proposition for him.
Link: http://archiveofourown.org/works/877568