At age 16, your girlfriend is getting drunk on a recurring basis? That is very worrisome. This girl needs help. You're trying to help a situation that is beyond you. I understand that, if you're in love with her, you're not going to leave her. She's fortunate to be loved like that.
It would hurt her, if you broke up with her. The longer this relationship goes on, the harder it will be, if you were to leave her. You're taking on a lot of responsibility. The price of you doing that is going to be quite high.