Been there OP, Ex was a very selfish man who always put himself above me and the kids and in the end i withdrew from him. Breaking up our 23 year relationship was the hardest thing i ever did and it devastated me.
I knew deep down that splitting was the right thing and after all his EAs over the years i didnt trust him and i knew i would get through it and be happy.
But fuck me op, what a rollercoaster, i was so upset, everything happening was like a body blow, collecting his things, finding out that only 6 weeks of moving out he moved in with his EA partner, splitting the bank account, changing my NOK on everything, removing him off the car insurance for example, it was a constant churn of, this thing then the next thing then the next thing to deal with.
I cried all the time, i was so hurt and second guessed myself all the time, i regretted my decision a lot and the pull of 23 years was heartbreaking, BUT i knew it would never work and that kept me from embarrassing myself and begging him to come back. He would never have come back but would have enjoyed me begging.
Time OP, time is the only thing that helps. And keep in your mind that YOU chose this and remember WHY you chose it, the reasons why YOU decided to end things and the bright future you can have. Keep dreaming of your shiny future, ride out the bad feelings and the upset and it will get better.
My favorite quote "Sadness flies away on the wings of time" helped and off loading to friends and family.