In my opinion, you are doing as he wishes by leaving him be when he asks you to. By later blaming you for not contacting him is extremely selfish in my opinion. Have you told him that you were only doing as he wished? How long do you leave him to his own devices before he contacts you? PTSD does cause this to happen, in my experience anyway. However if he is amking you feel bad for this it is not ok! However I have experienced it and I know how you are feeling. Maybe you should just dit down and talk to him about how it is making you feel. Tell him that you will be there for him but that you don't want to interfere when he wants his own time.