Welcome! I've known and been in a relationship with my sufferer for a little over 4 months now. Obviously every relationship is different, especially with PTSD depending on his situation.
I'm still relatively new to it myself, but from my experience my advice is to be ready for anything. And definitely try not to take things personally if he isolates, or goes on a tangent about how you can do better, etc. There have been *countless* times I've found myself crying to my girlfriends about "He hasnt talked to me in 2 days!" and you come to realize it's nothing personal, you just need to give him the space if and when he needs it.
Also, do your research on PTSD as much as you can and search around the forum, theres a lot of fantastic insight here from people who have very successful relationships with sufferers. This is a great place to come when you want to rage out on him for something he's done (be whatever it is) and the people here are extremely supportive because we're all in the same boat. Also be prepared for some of your friends to not "get it." I've had numerous friends who have always "been there" for me tell me "Why do you deal with it? Relationships shouldnt be like that," etcetc. You need to have the skin of a rhinosaurus but at the same time dont walk on eggshells either.
Hope that helped. :barefoot:
-JS