I am looking for a specific story.  When Sam runs away to college he meets an old woman on the bus who accidentally erases his memory.  She pretends he is part of her family and he goes to Stanford.  Dean comes around to check up on him and realizes he has no memories of Dean or their life.  Dean crashes with him and they hang out at the college bar while Dean continues hunting and tries to figure out how Sam lost his memories.  I am pretty sure it was wincest but not 100%.