But in your specific case OP I don't think it matters - you aren't his psychologist.
He does what he does because he likes it.
He won't change - so you have to.
I suggest you changed by running for the hills.
It will only get worse, not better and times of stress will increase his urges further.
If I remember correctly he works in a care home? Plenty of opportunities to humiliate and ridicule.
Of course he's 'good' at work as far as everyone else is aware, he's cunning. He wouldn't get away with it if he was stupid.
I honestly worry for you OPk.
Has he put his hand around your throat or talked about how easy it would be to kill you?
I'm thinking yes.
These are massive alarm bells.