If you defeat or dominate Vicoria rewards you with 20 dislikes from Ste. Months ago, when I tried to have sex only with Vicoria I couldn't. Maybe you need enough likes with her, but I'm almost sure you can't because (spoiler) if you have a threesome your sanity drops to 5 and Arion saves you before you go insane, indicating that if you have done this alone, you would have got insane.