@B.J. All of the above is why I asked you all those questions that could help figure out if this is isolation we're talking about or a breakup. The distinction is important, not in order to gauge how horrible/unforgivable/insert terrible adjective your "mistake" was, but to adequately help you find a way to understand what is happening and choose a way forward accordingly.
You haven't answered any of those questions, maybe in part because you don't want to hear that this is over and you should move on. Most likely, with the guilt you're feelings, you'd equate that response with your mistake being unforgivable.
Objectively speaking, and this is just my humble opinion, your "mistake" is not unforgivable. This is looking at it from the angle of a normal relationship that operates on rational, pragmatic terms. Unfortunately, our PTSD relationships are rarely rational and pragmatic--and that to varying degrees--so really our view on what is and isn't forgivable goes out the window in relationships like these.
I think the goal is for you to forgive YOURSELF for what you did. For that you need to first come to terms with what is happening now (thus my questions to you above) and then find the compassion and understanding for YOURSELF of having done everything possible in an impossible situation.
As much as all of us would like, this forum isn't the Oracle of Delphi. We can't say if he'll come back, if this is just another sufferer isolating, or if if it's more final than that. But I assure you, even if it's the case that he broke up for good, none of us here would tell you to just get over it.
I know I've made mistakes with my sufferer. Yes, he's told me xyz was "the most horrible thing anyone has ever done to him." But that was trigger talk, and he may have isolated after, but it didn't take a lot of coaxing for me to make him understand that it's nothing to break up over.
On the other hand, I'm pretty sure there are a few things I could do where he would break up with me and never look back. He has a hard time trusting people, is insanely stubborn, and there are a few lines in the sand, when crossed, there would be no way back. And it wouldn't matter a bit if what I did was objectively speaking not that bad. He'd be done, fin, fertig. Living with that would be sheer and utter hell, and despite having done EVERYTHING for this relationship,
I'd be left feeling like it was all my fault.
That's the belief that any supporter who has been broken up with needs to take a hard look at.