Aaagh - typed a long, considered post and then Mumsnet went off for maintenance and it was lost!
Tired, as you know I've been following your story, so here is my advice. You can tell the truth, while retaining your dignity and not coming across as a victim.
This man toyed with your mental health, never came clean about his misdemeanours, it took OW's husband to expose his lies - and instead of being honest with you then, he started a smear campaign against the man he'd cuckolded. This poor man also told you that he thought your H had engaged in yet another affair, before the one with his wife.
I told you once that men like this - men who care desperately about "appearances" distort the truth and try to make out that "they tried very hard to save their marriages, but in the end, the love just wasn't there. By some absolute miracle, I then met up with Miss Wonderful, who coincidentally, had just left her own marriage..." No-one's going to buy this for a second, Tired. I'm sure his family are "allowing" him this fantasy, because it suits them not to "own" having an adulterer in the family. But believe me, when a member of my extended family did this to his wife, my first question was "So who is she?" - and I was right, of course.
You are making the absolutely right decision to move nearer to your family. You need nurturing and caring for at this time like no other. However, there will be some misguided and ill-informed people who will criticise you for that decision. That's why exposing your H as a fraud is important.
I don't think it will affect the divorce one jot if you tell the truth. I think this man will behave like an arse during the divorce proceedings what ever you do.
Your nearest and dearest know the truth. To others, I would have absolutely no problem with saying: "I tried very hard to save my marriage, even after discovering there were other women. However, in the end it was my husband's decision to end the marriage and actually now, I do accept that is the right thing to do. I now want to move on and create a happy family life for me and my children."
This is telling the truth, with great dignity and no victim status.
Oh and I might have suggested this line to you before, but if you ever have a calm conversation with your exH, try saying this, with a smile on your face:
"I now realise that you were not meeting my needs for some time - and I'm really excited about giving someone else the opportunity to do that."
Don't suppress your anger Tired, give vent to it. Come on here for support and start those moves back to your family.