He is so much a part of me that not only can i not enforce boundaries, i feel bad when i do.
There's your problem right there, as the mechanic said.
It sounds like the first boundary you could consider is one that separates the two of you as individuals. If he is "a part of you" you can no more have boundaries with him than if you're trying to set a boundary with your own body.
When I left, my ex wanted me to go to counseling with him. I didn't. I went to counseling for myself instead, to -- as NYCDoglover said -- figure out why my self esteem was so low that I thought it was appropriate for me to be treated like I was.
And forgive me, but I've grown a bit cynical with time:
I think about how much he loves our children,
Apparently not more than his booze, though, or he would get help.
and
I think about how horrible he feels when he drinks too much and yells. He knows how much it hurts us, i can see how much it's wearing on him.
Do you know that he could change this if he wanted to? I wouldn't feel too sorry for him. He apparently doesn't feel it's enough of a problem to warrant changing for.