Everyone drinks, dont know why this is a big shocker to you?? If she cheated on you after you spent 2 years workin on gettin with that, then its not worth the time. Dump her. Your only 17, tons of other girls to pick up.
If you have been dating 1 month, but she cheats on you in under 1 week, and she has emotional stress issues from her family problems, I will be honest and state she isn't worth the time investment. I am 18, and live with my g/f, but 90% of the time, people our age do not know was 'love' is, and just want to jump onto the 'happiness' (and believe me, love is not the pure happiness you see in the movies, its FAR different) that everyone thinks occurs when your meet 'the one' (which, at our age, is basically each boyfriend / girlfriend we get). Personally, I don't respect, nor do I look at cheaters. No one has ever cheated on me, and I have dated my fair share of women, but if a girl did cheat on me, it would be over like that *snaps fingers*. There are plenty of women out there whom are attractive, won't treat you like ----, and won't be those emotional and clingy girls everyone hates (which, if her dad beats her, shes going to be that way).