I would be very careful, even though it has been 3 years this sounds like the start of an abusive relationship. When one person thinks of another as a possession it can get really scary. He has already cheated on you, he has shown that he does not care for your feelings and even brings up trivial little things from months ago to throw back in your face. You leave and he is all apologetic and nice but then he gets abusive again , you leave and he makes promises to win you back. It cycles and each time it escalates and you are drawn in even deeper. I hope I am wrong. There has to be some boundaries. It is just my opinion but it sounds like he is using his ptsd to keep you on the hook instead of working to get better by guilting you into taking the abuse.It came to surface because he was having a very hard time accepting that I had been with another man, as in his mind I was, and always had been ''his woman''.
He always says: When im better, you will see how I will treat you like you deserve to be treated.
Does this mean he knows he is treating you badly and that he can keep treating you badly as long as he sees a psychiatrist without telling the doctor why he is there? He hasn't been diagnosed, you can not diagnose him. If he wants to get better he needs to open up and get a diagnosis and get the proper treatment. He may not have PTSD, you are just assuming he does and he is milking it for all he can.