Anger At People who Made It Worse

This thread contains mentions of extreme violence and abuse. Please proceed with caution.

Lately I've been thinking and getting angry at my ex's mom. When we were together and he was abusing me, getting back into drugs and drinking alcohol, not going to see his psychiatrist etc, I would text his mom to inform her of his actions. At the time he and I lived in an apartment together and his parents paid the rent.

She would call him immediately and say "KD told me you bought drugs". He would then get mad at me.

One time he decided to use my phone to type out a message telling her I made a mistake and that he didn't buy drugs. He wanted her to believe I wrote the message. He said they were going to take him out of college if they found out. He badgered me into letting him do it, and after he did I discretely emailed her to tell her it wasn't me who wrote and sent it. She immediately called him and said "KD just emailed me to tell me it was you who sent the message" . I was pretty scared he was going to beat me.

The last day of our relationship, when he beat me and threatened to strangle me, I texted her to beg her to call the cops. She called me to ask what was happening. He pulled the phone away from me and broke it. She then called his phone and told him she called the cops because I texted her. He hung up on her and then backhanded me across face.

It was her fault I got hit. I'm still mad at her. She was incredibly stupid to do that. She almost got me killed. I want to get past this and learn to not be angry anymore. How do I do this?