I am in very much the same situation- we agreed to amicably divorce in December after a 6 month separation. We filed the first papers in March, pledging that we still wanted to be in each others' lives. I learned a few months later before the divorce was final that he had formed a new relationship that he didn't want to 'jeopardize' by entertaining the reconciliation I proposed. So I think his relationship is moving fast as well. He noted on his social media profile that he was on dating apps in February. To me, it's now clear he started grieving our split as soon as we separated- the divorce itself was a formality to him and I understand that. But I don't have to overlook it. This of course threatens any possibility that I remain in his life to any degree as we share no children.

I, like you, am hurting massively from this- the worst emotional pain of my life hands down. And I may not ever be able to bring myself to see him again, and that's okay. I sometimes envision him and his girlfriend together- and believe me it can't be a bed of roses for them. He hasn't invested any work into reflecting on what he could have done better in our marriage as I still encountered the same thoughtless behaviors from him after the divorce began. But that's not my problem now. His emotional health is not mine to worry about any more. His physical health or anything else I used to have to care for about him isn't either. It's a hard realization, but it's true. The sex we used to have that wasn't all that great for me? Not my problem any longer either. Thinking about these things has very much helped me hate him and even the girlfriend less. Those kinds of relationships are just risky as hell.

Once I found out about the relationship I told him to come and collect his things from my apartment and settle our remaining accounts. He dragged his feet and went radio silent until I took the initiative to tie up all loose ends so that I could go no-contact from him. I am currently on day 12 of no-contact to better reflect and get over my own grief, and just in the second day I already began to feel better. Even my appetite was a little better. I know you have kids, so make those transactions with him as businesslike as possible, cordial, with as few words as necessary. Don't ask your kids about him or his girlfriend and if they want to talk about it, promise them that you will in a month or two. You are doing the right thing. Don't lose faith in all men- just the one who caused you so much pain.