Hi Holymoly
re your comment:-
"@AttilaTheMeerkat you’re right, I think I’ve stayed because he’s all I’ve ever known and the alternative of leaving him seems scary. And all I can think is it will break the kids hearts cos even though he isn’t the best dad my eldest dotes on him the most".
And what about your youngest?. You've already seen the hurt in your eldest son's eyes when his dad says he won't take him to football so I doubt very much that your eldest dotes on him (that is merely what you assume of him).
The alternative of you staying with him for your own reasons and sake (and it could be argued its for your own sake rather than theirs) is far more scary to my mind. Your H is a dictator and joy sucker of life and as your kids get older, they will further realise just how crap he actually is as a father.
Staying for the sake of the kids is never a good idea and in your case a particularly bad one, its a terribly heavy burden to place upon your children. They will also look at you and wonder why you are so weak and have put him before them. So your own relationship with them going forward could be affected to its detriment if you stay and just because you are scared and its all you've ever known.
Time to expand your horizons far more here. Change and separation is difficult I grant you but this is no marriage model to show them and you're selling your own self short in the process by at all staying with him. You would not even be staying with him for your own reasons either.
Is this really what you want to teach your children about relationships, they are learning about relationships from you as well here. Its a terrible legacy to leave them, you want a crap and otherwise loveless marriage to be their norm too?. No you do not. Would you want these children to behave like their dad as adults, no. But you're showing them that currently at least, this relationship is still acceptable to you on some level.