I've just come to this thread. Only read OP comments.
I have to say that a few years' back, I would have been on the side of 'you can't risk him hurting you and the kids any more / it's unreasonable and crazy to expect you to have him back.'
But now I think differently. As a result of what's happened in my life.
You were at a stable point and everything seemed fair on the horizon. Then suddenly, completely out of the blue, a massive wave hits you and shocks you practically out of the water.
The tricky thing here is that he was the force behind the impact. Him, or, at least, his mental state.
Look at two things:
Setting aside the hurt and outrage for a moment (...), what situation would give the most certain happiness, opportunity, security and a good life for you all? Presumably if he was back and normal and all this had never happened?
You've been together for nearly 20 years, adding a bit of time pre-marriage. If you had a mental breakdown, however messy and dirty and painful that it was, would you expect him to give you the benefit of the doubt and see you through it?
Sometimes something crazy happens. I've observed that the male process of midlife crisis can be catastrophic. But weirdly after a bit of time they seem to calm down and wish they were home. And they want everyone to forget about it.
It's up to you, of course.
But given all the good at play here, and the uncertainty of life without the family unit, for you as much as the kids, I personally would want to take him to the gp and see where that leads.
As you (not unhinged like him) have very rightly felt, there is a huge amount of the most precious elements of your life at stake here. And this 'blip' seemed to have no reason to it.
Incidentally, I've known at least five women go through something roughly similar (although always involving at least 'chat' with an OW), and them packing bin bags and him living in a hotel or flat, and then I've been astonished when a few months' later they're all calm and he's back in the fold and it's better than before, he's on parole and much chastised and grateful, and their life goes on and they go to their kids' graduation ceremonies and weddings and have a warm body next to them at night and someone to put the rubbish out.
And you don't have the clear attack of an OW in this mix, which is pretty good, I can tell you.
I would welcome a medical opinion on his bonkers behaviour, and would be wheeling that bugger down to the gp. Or for a virtual consultation ...
I think there's too much at stake. Having been on the other side and lost my whole base, I'd say keep your base. Which includes him. Women do, and it can and does work out.
That is my very possibly non MN-PC, but practical, advice. From experience.