It's easy to understand. He's a mean, manipulative @$$hole who makes himself feel powerful by bullying and intimidating others.

Things like this aren't usually caused by a mental disorder, but even if it were, we need to let go of the notion that we must put up with somebody's behavior just because they're "sick" and "can't help it." What if it were a different set of symptoms? If this man were prone to hallucinations, and thought your baby was a poisonous snake that was biting you, of course it wouldn't be his fault. But you wouldn't just stand there patiently and let him harm your baby, thinking he's killing the snake, would you?

The best thing you can do for your teenagers AND your new baby is to get away from him and don't look back. Document everything so he can't lie about it later. Because if you stay, you're teaching sons that this is how they should treat women, and you're teaching daughters that this is how they should expect to be treated.