Anybody any advice (sorry for my English)?

Whenever my boyfriend does something I didn’t like he finds a way to turn it on me. Like for instance I also did it once or I was the one that started. Which isn’t true but I almost never have a way to show it. Luckily a few times the discussions happened by text and then I can show him that I never did or said that. He then calms down and say sorry and everything. This form of defence is something he got from all his childhood trauma. He has cPTSD. I know this is something from his past. But it really makes me sad. Because he makes it worse and I become sad because I don’t get why he doesn’t get the point when we are arguing. Also after the discussion I’m every time left sad. Most of the times he forgot he did something, also something from his trauma. That’s why I’m also most of the times left without explanation and I just have to accept his apology and move on. It really hurts me because I never get an explanation and have to prove myself. One time I talked to him about it and he said that he is working on his past. Does anybody has any advice on how to corporate. We are planning on getting relationship therapy after I had to plea to him.

Anybody any advice (sorry for my English)?
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