You are getting between him and the most important thing in his life...his next drink. He wants to remove you as an obstacle to continue. It's his right as an adult to screw up his life so far as the law will let him, don't hold it against yourself as you didn't cause the problem nor can you fix it. It sucks to hear, but in his world the only thing that matters is drinking, relationships with others be damned. (I'm one w/ drinking problem personally and despite the situations being different, our thought processes tend to be the same regardless.)
He might come to his senses eventually and never go back...or just continue until who knows what happens (something bad to be sure). You made a fantastic decision to no longer be part of that. Best of luck moving forward with your and your daughters lives, him being around likely helps skew their mindset of what is considered an acceptable relationship.