Pls see my post about "why doesn't he/she love me enough to quit"...there are a lot of people posting on the end some really helpful things about what happens to children living with an active alcoholic.
it's not pretty.
I agree with the others-guilt is not productive. There's no reason for you to feel guilty--I'm sure there were good things about him at one point, and maybe even still. I could see past my ex's drinking, to see who he really was underneath the disease, quite often.
But the pain of leaving outweighed the pain of staying. I do not consider it a mistake because I had a lot of good times with him, and I learned a lot from him, believe it or not. He did bring a lot to my life besides pain.