"It was just me I would walk but I can't stand the thought of the DC growing up without their Dad around".
Did you grow up without a Dad?. Is that why you hold that opinion?. You don't have to answer either question.
We learn about relationships first and foremost from our parents.
I would argue that their Dad is not really around anyway is he if he's drinking that much every day. He's taking no real notice of either of your two children is he?. And he treats you with utter contempt.
What is better; two parents at war with each other but "together" (staying together for the sake of the children) and two parents apart but ultimately happier?.
What lessons are you both teaching your children - damaging lessons are being imparted here to them; ones that they could well go on to repeat if no solution is found.
He's showing your two that he can treat Mummy like something he's stepped and Mummy accepts this.
Many women in an abusive relationship like yourself use the "well he's a good Dad" because they have absolutely nothing else that is "good" to say about him with regards to relations with their own selves.
Your husband is a deeply unhappy individual; I would also say a controlling one. You cannot fix him so don't even try. Controlling men are often very angry men too.
If he won't go to Relate (which is not surprising really given the fact he does not seem to think he has a problem) consider instead going on your own and discuss these issues with a counsellor.
Your children and you deserve better than he.
You actually can change things for the better for you and them; you just have to start believing in yourself, recover your self esteem and making plans to separate if this is what you ultimately want.