BTDT. I was on the verge of that breakdown for a long time. Like those before me, I learned that if I took him out of the equation my life was much more peaceful. I had security, dependability, accountability, etc. Your life can work no matter what he does as long as you don't count on what he does. You can make it so you don't have to count on him.
I moved out of my dream house and to a smaller town so I would not have to count on his child support. I paid daycare so I would not have to count on his parenting while I worked. I also didn't have to worry so much about him showing up on my door step. I did not make commitments or plan personal time unless I had a babysitter or other arrangement. If he was supposed to pick them up at 10am and I had a commitment that day I emailed him and said I had to leave at 11am (or whatever) and if was not there by then I would take the kids with me. I did not plan things that the kids couldn't be along for.
A big part of what my xah was doing was playing games with me. It was a big game to him to see how much drama he could create in my life. I didn't believe that at first but there was a couple times surrounding visitation that drove that point home. It wasn't about him or the kids, it was about me and making me 'pay' or manipulating me.
It works. It is such a relief! He moved far away now and I am really and truly all alone - and that is even better. I don't even have to think about accommodating him. He is apparently sober now so it might not be better for the kids but it isn't my life so I no longer spend time thinking about his choices. They are what they are.