Sorry, I forgot to answer your question.
"But he has a way of breaking me down, to feel like I am the worst person in the world. No one else makes me feel as low as he does. How did you get through this?"
By getting and staying as far away from the people who make me feel like this. Do you know the Serenity Prayer? It is at the bottom of my posts. Through working on me and working on my Recovery, and by practicing, have begun to learn what I can control and what I cannot. I know that when my interactions with people bring me pain, panic, despair, confusion, or just plain bad feelings, and I try to make some adjustment but it doesn't change, that that person is toxic and there is nothing i can do to fix or change that. It is out of my control. What is IN my control is whether or not I will continue to have that person in my life and how much.
I hope something I have said is helpful. Take the best care of you you possibly can.