Hi dvd,
Please don't feel guilty. I assure you she is the one miserable with herself and more than likely the alcohol is what is causing her depression. She may not want to admit that, but until she's ready to seek out help, nothing will change. You moving on and wanting happiness is nothing to be guilty about.
As mentioned, do find a means of support for yourself, in your area. It's okay to walk away, when someone is slowly killing themselves, you don't have to watch anymore. *hugs*