GG, What you are going through is terrible. I feel truly awful to know this is happening to you. I understand very well how you feel at this point.
My X was criticizing me constantly after she left. We had joint custody. I was doing my best to keep the kids routine normal. She and her mother would complain about me to the kids. She would bribe them. She would .... Finally, I started doubting myself and making little mistakes. Hardly noticeable at first. She would pounce. I would start second guessing myself. She would pounce again. Eventually, it took its toll and the kids began to want to live with mommy and grandma full time. So I had to make a choice.
She came to me one night and told me the kids wanted to live with her and grandma full time. Instead of arguing, I did what I thought was best for them and said yes. Maybe I was wrong but who knows.
Anyway, that wasn't good enough for her. So she immediately filed for full custody and in doing so listed a lot of really distorted things to get what she wanted. It wasn't enough that she had essentially full custody already and a fully cooperative parent. No. It had to hurt.
So here we are to today, I have washed my hands of her. She is still bitter and angry. My R with my kids is steadily improving...because I just ignore her. I am becoming confident again.
There were many times she threatened legal action and I would cower in a corner because I was trying to do the right thing for all of us...appease the unappeasable.
It takes time but you will find a way. Once you no longer fear his control over you, you will regain contro of your own life.
