That's cool man. Most definitely. I mean honestly it may not be an "alcoholic" we are dealing with, but simply a girl who likes the party, likes the attention, likes the freedom, and so on. Alcohol is an escape, but so is a new relationship, a new guy, new friends, new places, etc.
Overall, these girls are not ready to settle down and they are going to run and escape any way they know how. I am trying to look at it that way. My case was rough because we lived together for 4 years and have been engaged for a year and a half. If she wanted out of this life she had plenty of time to do it in. But still like people say, better for them to leave NOW then later, even if it wasn't as soon as you thought, anyone capable of doing the lying/cheating thing, it's in their blood, in their brain, if they didn't do it now it would have come later...These people don't face problems, they run from them, they use alcohol as a way to numb the poor decisions, they rationalize it however they can.
I am all cool with a girl who says she doesn't want to be together anymore, that is a mature, normal decision to make. I am not cool with a girl who cheats and lies and sneaks around and doesn't tell me what's going on. Regardless of the booze the lying and deception is what made the break something that had to happen.