Hi Skribble
This happened to me a couple of years ago (minus the other woman, all the other stuff the same) plus it's happened with several other people I know I think you're right to hang in there, there's a good chance it will work out. The main things I've learned or suggest you think about are these:
You can't control your DH or what he does, at this stage, if you try to make him do anything he'll resist more and go the other way.
You need to look after yourself and and find out who you are and what your purpose is - new hobby, job, back in touch with old friends, exercise, looks etc. You need to become the woman you can be (or used to be)
Let him have the space, move out etc. and make it clear you want the relationship to work, but for it to be a good one (you won't be a doormat), so you both have to change and that it could be wonderful.
And it's right, you will have to be the strong one, find friends who will listen and support you. I phoned the Samaritans several times as well.
And as and when he starts to engage again, look at what both of you did that contributed to this.
My DH left, he was sure it was over. I remember saying to him "I can't and won't walk away from this marriage, it won't work I know unless we both change, but I want the fairytale" Also made new frineds, bought new clothes (only for him initially but slowly became for me) we went to relate and talked honestly for the first time in years back to square 1 about what we wanted from our lives, which we were too scared to do before and didn't know how to.
It was the worst year of my life, but the best thing (in a funny way) that happened to our relationship. Looking back now he can't believe he was capable of what he did, but he also had so much pressure at work, with his life (and from me) that it was almost a breakdown a bit I think. Also maybe a bit midlife crisis.
So (sorry long post) it may be OK, it may not, but it's certainly not definitely over.
I have the fairytale now, and a whole lot more relationship skills!
thinking of you