Correction: if you win against Vicoria and release Ste, he will say he was always a guest in the dungeon and the succubus was just lonely. He will then stay and tend to her. Even if you win by lust (and gain a like from Vicoria), Ste finds her unconscious.
No matter how much I raise the Endurance stat, Vicoria just says something to the effect of "now this is a man", says she wasn't satisfied but that you did more than well.