I may have missed some info; whose kids are they? Hers, yours, both of yours together? This may complicate your break up.

Her controlling abuse built up over years because you accepted it. Had she tried her control tactics, and you flat out told her, "You do things your way, I do things my way", the relationship might have ended right there and then, or she might have bent to compromise.

I'm not victim blaming. I'm just pointing out, that she is going to be shocked that you've suddenly taken notice of her controlling ways and found it so unacceptable, you are leaving her.

I agree, she probably can't change.

You tried to be a nice guy and put up with a whole lot, until it got so out of control you couldn't take any more and had to leave.

I guess I'd explain that simple truth to her. I hope the leaving process goes well for you and for the kids.