tl;dr Women will ignore signs of incompatibility and mental illness if he's good looking enough to give her those tingles. Muscles beat brains often enough in attraction.

So, you're saying that your excuse for staying in the relationship was solely based on his looks. Even though he had obvious mental issues that inhibited his judgement and behaved in strange ways, she "never had a man that good looking before to give her those tingles". This is what the average guy is up against with muscular men. There is just no competition. Women will literally pull the wool over their own eyes if they can get a glimpse of the angle they want to see while doing so.

https://www.youtube.com/watch?v=rUWReitzR5A

Lessons learned: Lift, get big.