You’ve just got to rip the plaster off and do it. I’ve been there. Mostly waiting for a big argument to be able to put it out there. In the end it was over something really petty but I’d had enough.
It felt like I was wearing a huge heavy coat and when he finally left I was able to take it off.
In my experience when you go armed with a plan they totally refute it because you’ve come armed to a fight.
Put it on the table that it’s over for you and see where the conversation goes.
Plan for if he is a complete dick, won’t move out, won’t accept custody arrangements, plan for the worst outcome.
Then you will have your starting point.
Figure out where you would go if he won’t leave
Can you support your self - would you need UC?
Check what your entitled to on a benefits calculator.
I like being a single parent. I don’t think I’d ever live with a man again. My reality is real.
I also read a book called ‘too good to leave too bad to stay’ and I knew I’d have a happier life with out him. I deserved to be happy. Once that was solidified in my head there was no going back.
Good luck 