It isn't alcohol that's the problem, it's you. Many years ago a girl told me "A drunken man has a sober mind". Basically, when alcohol takes away our inhibitions, the real person comes to the fore.

You need to learn why an 18 year-old wants to go around biting people.

You don't have to tell anybody that you're a lesbian as you don't know for sure yourself. Just explain to the guy that there has been a misunderstanding, you want to be good friends, but no sex or commitment. Keep things simple.