...Adam really was an evil GF, wasn't he? And I think losing their shared growing-up-together memories would definitely lessen the sense of incest, whether they were biological brothers or not.

(You know, I stumbled across a fic in which Sam lost his memories and fell in love with Dean, not knowing that Dean was his brother, and Dean, who hadn't lost his memories and was perfectly aware of Sam's amnesiac condition, agreed to have sex with him. Gigantic moral squick.)