Bio/History: Wolfgang was always born with two personalities, a good and bad. The bad side of him always stayed dormant, but stirred up from his sleep from time to time when the good Wolfgang faced internal struggles. The bad Wolfgang would whisper to do evil deeds and would even temporarily take control of the body to make those deeds happen.
Another way of telling which personality is in control of the body by looking at the seven wolf demon's appearances. When the good is in control, they retain their original appearance but when the bad is in control, the demons gain a more demonic appearance with a dark aura following them.
When he was faced with "rejection" from Nien, he became emotionally weak/faced internal struggles and the "evil" side took control of the body and raped Nien but the "good" was awake and was trying to fight the "evil" side. When the "evil" successfully raped Nien, the "good" couldn't believe he did that and officially caved in.