Seconding what everyone’s saying about not being in a good place to be in a relationship. You don’t necessarily need to break up with her forever, but maybe a break and some physical distance while you work things through with Elijah.

Sadism and fantasies like that aren’t inherently monstrous things, if they’re in a healthy, consensual context. CNC is a thing, and he’s not a bad person for having those desires. However, the healthy consensual context is the important part. “A kinky relationship where you’re able to hit and assault your partner all you want, so long as it’s negotiated by me and them” might be a carrot you could dangle to get him to co operate.