Why TF am I still dating him?! [Serious]

Can someone please explain to me, why am I still dating a man who is extremely toxic for me? He used to be physically abusive, was and still is verbally, emotionally and financially abusive? Who is a severe (clinical) NPD? Who is degrading me, disregrading me and hurting my self esteem? Who is NOT pleasing me sexually? Who is in fact extremely high maintenance (without a reward)?

Together for 4 years, live together, work together.

It's like I know he is bad for me. It took me a while to understand that it's not me. It's him. But after an entire year of knowing the truth (that he has severe npd and that I'm not crazy), I still can't wrap my head around why I'm still with him.

I can't leave him. I have no idea what's stopping me.

Am I taking pleasure from this torture? Is this really what I think I deserve? Do I think it can be worse? Am I afraid of making the wrong choice (if I leave, I lose)? Am I caring and think he deserves someone like me who understands him and treats him well? Am I used/addicted to this?

I have money on the side. I have places to stay.

Please help me understand why I haven't had the courage to leave. I know he is toxic. I don't know why I still can't let go of him.

We do have good things too. Of course it's not all bad. But the bad is unnacceptable and I know that. Which is why I didn't say anything positive, as that would be justifying.