Yeah I do understand....I was with an alcoholic for 3 years. I was very much in love with the man although I knew he had some serious issues. Tried to cut it off and he kept begging to come back. We broke up in July finally after he had a huge fight. I could not take the verbal abuse and obscenities he hurled at me. I became very anxious and depressed. Finally that gave me what I needed to cut the cord. And I should mention I finally got angry at HIM in return -- and he could not take it.
I highly recommend individual counseling if you can afford it. I have been in far too many crappy relationships for too long. What is it that you see in this man? Are you really in love with him or just afraid of being alone? (Similar to what Pelican said above).
I believe when we truly know we will be fine on our own, we will stop attracting bad people into our lives. That's what I have been working on lately myself. I also recommend you do a lot of reading on Codependency, especially the books by Melody Beattie.
(((hugs)))