drummer, you're being a little hard on yourself bud. SHE was the one with the drinking problem, it created a lot of drama between you and even when you expressed that it bothered you, she refused to quit. in fact, she left.
sounds like she's been a party girl all along. and has a "lifestyle" that is centered around drinking...working at a bar, freinds are all in the bar scene, and those are who she went to immediately.
i'm so glad you are already taking positive steps for YOU! as time goes by you'll be able to look back over the time you guys had together and be a bit more objective (not that you aren't NOW, you're just still deep in the sea of emotions!) and the gild will be off the lily and it might not look as fabulous as it FEELS right now. you might see her in a different light too.
bottom line - people break up all the time. for lots of reasons. this does not diminish your experience, just might help with perspective. you'll get thru this, one day at a time!!!