Lavender, have you thought that lots of people simply decide they don't want to be in a relationship with someone for no particularly good reason? The relationship is just not working, for THEM.
And that to break up the relationship and be on their own is completely their right.
They may feel that, morally, they ought to give their ex-partner a reason. But after that, really they have no obligation ever to talk that person again (apart from facilitating contact for any children, which can be done via a third party).
When the ex-parner is a decent, nice person who has done nothing wrong as such, this is very hard for them. But they have to work through it and get over it on their own. We have all been there, been dumped, and it is horrid. But we know as grown-ups that we just have to battle on and try and get over it. We take responsibility for our own lives and emotional wellbeing.
In your case, the ex-partner is quite clearly a complete and utter scumbag. So WHY are you giving him so much more air-time? Why is there any need for you to speak to him at all? You can communicate via a solicitor perfectly well. You can use your email address to deal with contact from him - only log in once a day/week/fortnight/whatever. Then get a new email address to speak to everyone else. Ditto phones - get a cheap payg mobile and switch it on at certain, agreed times for him to speak to the kids. Change the house phone number and your current mobile.
And fgs get the divorce underway. Without it, he can turn up on your doorstep whenever he pleases and insist he stays. With it, you don't have to face that. That seems a big difference to me.
You are currently doing the 'I will take responsibility for YOU seeing your children' dance. And it is because you love them so much. But it won't work, they won't be any less hurt by him over the years and he will use it and use it and use it to manipulate, hurt, upset and crush you.