I think the one thing that has helped me heal from being with abusive ex is self respect.
It's less about understanding the psychopath and more about what it was in me that called to people of his ilk.
My empathy. My caring nature. My capacity to forgive, and my innocent, trusting nature. All wonderful qualities.. But
That innocence is gone, and in it's place a darkness that I wish I didn't know existed. But it does, I've seen it. I have boundaries in place to make sure it doesn't happen to me again. I also Have spirituality enough to know and to feel, and to heal. Ex does not have that, will never have that, and will continue the same patterns of use and abuse.
We can overcome what has happened to us, and be proud that we survived. We are survivors.