Fiance has PTSD...

Last December in a armed robbery my fiance got shot through his pelvis, unfortunately leading so nerve damage and paralysis. I urged him in the following weeks and months to go talk to a therapist about what happened . He assured me he didn't need to and that he was fine and dealing with it in his own way. Which appeared to be true until this last week or so. Hes been having nightmares every night and panic attacks during the day. He says when he notices something as simple has me leaving the door unlocked he gets EXTEMELY angry. At this point I feel useless , I want to take away his pain so bad but I just don't know. Should I keep on him about going and talking to a therapist , or is this really something he can deal with on his own. I just need advice.