Anger and frustration within relationship

I, autistic, 24, am in a relationship with someone who is 25, not autistic. It's my first relationship, ongoing for 4 years. 

When we have discussions about certain topics, I feel such internal rage I could implode. For example I think she is in an emotional abusive relationship with her therapist (probably narcissistic) but she (the gf) has such intense blind spots about it she hasn't been able to leave the relationship yet. (Some people have said it's like a trauma bond or smth) 

Sometimes we will have good conversations about how her therapist isn't good for her and she'll see the points I'm making, and then other days she will defend her therapist and not listen to a word I say. I don't understand it anyways, I don't understand many of her feelings and actions, but I've accepted most of it. But when she starts to deny things she has previously agreed to, I get so frustrated within the conversation and feel intense anger. It's like the situation is so frustrating bc it's a never ending circle of discussions. 

Has someone had similar feelings of anger and frustration with someone and learned how to manage them? 

I also struggle with anger rumination, once I'm angry it's very hard to be able to calm down.