If it was, as Drew stated, just for sex, then it should be possible to remain friends after the sex stopped.

HOWEVER, if there were "romantic feelings" a.k.a. "love", then it would be very difficult to return to "just friends".

I do have platonic female friends, and like Silverlock, occassionally have the "sweaty visions", but I know that doing so would change the relationship (and my wife would kill me)