Looking through your post history you note XH engages in coercive control. I also note you responded to Australian threads - some I'm assuming you're from here.
1800 RESPECT.
They are incredible. They can give you resources and support.
Especially around coercion and control - it's normal to feel like this. YOU ARE STILL BEING ABUSED. This is DV.
I get the despair. Walking away seems the easiest. You're at the bottom of a mountain, but you CAN scale it. If you want to. But it's okay NOT to, or not to want to. You caring so much makes you an incredible mum, and a wonderful human. This shit is hard, but your handling it. Maybe not to your own expectations, but you are. You're kids are loved. You're juggling life. That's enough.
If this is about your Dad's slip up. XH won't get 100% custody over that. It sounds like a regrettable one off and XH is overreacting. The guy apologised, has undertaken serious remedial action and it's a first "offence". Genuine remorse goes a long way.
I don't know how much you know about mediation - but none of it is binding. If you don't agree that's when they give you the certificate to say "this shit didn't work" and you can go to court. (Assuming this isn't court ordered meditation?) Mediator's can't force you to do shit at mediation. So don't be bullied. Collect every record you have of his bullshit behaviour and take it with you.
If it helps, the FCFCOA imposed parental training, drug tests and stringent rules about communication against the other parent in my case. Because I demonstrated coercive control through child related communications. If you want more info DM me. This is stress no person should have to go through. You stayed strong for 4 years. This won't be forever.