I'm sorry OP. I know it sucks and seems MOMENTUALLY unfair. It is unfair.
Ok but you've asked the right question, why am I repeating abusive relationahips?
The issue is, you're a target. To pick up multiple ones and have sustained damage means that in all probability, you're very empathic.
If you're abuse clear right now, then this is the time not to work on yourself par sae but to become truly self aware and guard yourself via knowledge on deflecting the two biggest Hoover's. The Seduction Hoover and the Grand Initial Hoover.
These two are tough to crack but there are ways and means.
People who suffer from NPD are not capable of love, despite what they might say. You are very capable of love. Too capable. Some of my kind talk frankly about what is sometimes perceived as a curse. There have been times when I have cursed it.
The effects of abuse make you feel utterly worthless and without value. This then makes you just a little bit more susceptible to the next one.
I have a friend who is aware he's has NPD and we talk lot. I also consult HG Tudor. There is a third who comes back around from time to time. I love that one very much. But he taught me a lesson, he showed me who I was and why I matter. That gave me back my self respect and helped me regain my dignity.
You need to flip it. Rather than seeing yourself as have no worth, know how unusual you are and That you're priceless. Read Tudor OP.