Sorry you are dealing with this, but I think you already know that you aren't comfortable with certain things about his life and lifestyle. That's okay! The whole idea of dating someone is to get to know them better and see how they handle life. If you are already having these concerns, I think you should listen to your gut.
As far as how to approach breaking up, that's up to you; however, just telling someone the relationship isn't working out for you is sufficient. If he presses you for more, then I would tell him his excessive drinking bothers me quite a bit. I'm pretty sure you wouldn't be the first woman to tell him that.