This guy I have discribed is mostly easy going, however, he uses medical marijuana. However, where his anger comes out has been fearing of being cheated on somehow. So, he has shown a temper.

It is important to keep in mind that there "is" anger with PTSD. I have certain things myself that can get me angry, I am working on it. You have yours too, it's just there in the mix. You just need to make sure his anger isn't toxic for you.
Sometimes these vets stray from therapy when they need to keep reinforcing healthy coping methods so they keep improving.

The important thing to find out though is if he is in therapy. You can be with him and maybe consider a relationship and even be supportive, but you can't take on the role of being his therapist, that isn't fair to you.