I did have a similar situation with my husband, years ago, after I left him in Cyprus (where he was posted), took the children and returned to Canada. He had been drinking heavily, behaving badly towards myself and the little ones. The final straw was when I caught him cheating on me. In any event, once he realized he's lost me, he followed me back to Canada and did a major turnaround in a very short period of time. Although he was being very lovely and very responsible and so on, I didn't trust him. It was such a major change that I was confused and uncertain much as you are. We were separated for 6 months, as I didn't quite believe him. It took me a long time to believe and trust him again. Fortunately in my case it was a permanent change.

Perhaps your being interested in someone else was the wakeup call he needed to smarten up? That would be the happiest explanation, most definitely. But whether or not it lasts, is very difficult to say. Best case scenario, he is truly trying to change. Worse case, he has changed to manipulate you into staying, and will revert to his old ways after he is certain you aren't leaving. I suspect it is somewhere in between the two. You must remember he is human and he has PTSD, so even with the best of intentions he may relapse. However that doesn't mean he won't now pick himself up again and keep trying. This could be a step forward in his healing process. My daughter has PTSD, and she makes quite radical changes every once in a while, which surprise my husband and myself. We also don't quite believe it initially, and often we are right, but often we are wrong too and the changes are permanent. It seems to be part of the ups and downs of having this illness.

How long has it been? As I am a mental health professional I would also wonder if it's not some form of manic behaviour. Has he changed meds recently? That can cause mania in some. Mania can make people very active and helpful for a short period of time. In any event, I would try to enjoy it while it lasts. It will take time for you to trust it, given his bad behaviour in the past. If he is indeed sincere it is certainly a marvelous change and I would praise him for it, perhaps that will give him more incentive to continue.