We have all felt the guilt. Its so hard to turn around and walk away. But, you get to a point where you have to realize that nothing you say or do is going to change this person. In order to be happy, you have to change your situation-that is all you have the power to do.
Maybe you leaving will be the swift kick in the ass she needs to get clean! In the meantime, work on you. Keep posting/venting, reading, get to some Alanon classes. It really does help.
As hard as it is, I have learned from the wonderful people on this site that no contact is the best way to go. It was very hard at first. But as each day goes by, it gets easier.
You deserve happiness...reach for it!