When you commented that he admitted to failing you as a supporter, I bit my tongue, because it was a good start.
But from where I sit, he actually needs to admit that he's failed you as a husband. Forget that it's PTSD for a moment - you're ill. What does a spouse do when their partner gets really ill? They find out what the f*ck is going on, how to treat it, how to help. Parkinsons, brain cancer, MS, ptsd - it doesn't matter. In sickness & health, because in life, we all get sick, and it's ugly and painful and unromantic. It's life. That's what you sign up for when you get married. That's the vow. "I'm gonna love you, right up till we're both old and not pretty any more. I'm gonna love you through the best times, and I'm gonna love you all through the worst times".
Counselling is great news. He's struggling. He's human. He's fallible. But part of him is still trying and that's worth fighting for.
But this isn't just about whether he can love you with ptsd. This is about whether he can love you, warts and all, period. He didn't live up to his end of the bargain. Saying he's leaving as a way to kick-start the conversation about what he should've been doing? That was him failing you. That's not how a marriage works.
I hope, I really really do, that you both get through this. But your value as a human, your value as his wife - don't underestimate that. Don't sell yourself short. You are worth loving, unconditionally. And that's what he needs to commit to.
I'm rooting for you. I'm rooting for the belief that it's possible for you two to survive this and be stronger together. Thoughts are with you MC.