No, it wasn't the ultimate trigger.
Siggy was evil. Jayden finally openly admits it. He was 'trying to reform'; at least, she thought he was. But apparently it's such a FRAGILE process that doing something like boinking your best friend's love interest wipes out all the good you were trying to do. Hey, cause, yannow, they weren't married or anything, just boyfriend and girlfriend. Getting between that - EVILEVILEVIL!
Hey, could Mookie be trying to say something about his life here? Yannow, cause he can't seem to keep a lady friend for long. Wonder why.
Edit: And -her- weakness? -Her- lust? Last time I checked, it took two to do that particular dance. Unless, of course Jayden found a way to rape Siggy.