As hard as it is for you to be going through this, I was so grateful to see that you have ended this relationship. No one could have said it better...you are just a kid, although you seem wise and kind beyond your years.
Stay away from her. Far, far away. This is a time in your life to have a zillion options and opportunities and to enjoy being young. This is no time, if there ever is one, to chain yourself to someone with advanced alcohol addiction. If she ever recovers, she has to do it on her own and by herself. Period.
You are a very good person and you have done the right thing for both of you.
Of course you will miss her, but at eighteen, relationships aren't meant to be permanent anyway. They are about learning who you are and what you want in your life.
I am impressed with your judgment. Good for you!