I feel like the worst girlfriend ever...

My boyfriend's 21st birthday is coming up in a couple of days. He and his friends are going to have a little get-together and there will be alcohol there. He promised me he wouldn't overdo it as he knows my disdain for the substance. I know I was supposed to smile to wish him to have fun before I go off to college for the week... but I couldn't.

I looked at him and said my fears aloud, "I've seen alcohol turn my father into the meanest man alive... I've seen my grandmother so drunk she couldn't remeber her own name... and that is all I see when I see those bottles... and I don't want that to happen to you."

I wasn't talking about just at his party, but in the long-run... I didn't want him to become what I had seen happen to the paternal side of my family. It's actually ironic: due to the events on my mother's side, I will never smoke; due to the events on my father's side, I will never drink. Their misfortunes and failing health taught me more about these two health risks than any health class ever could.

But back to the problem at hand, he tried to convince me that nothing will happen... to be honest I don't believe him... he's easily swayed into proving himself to his friends and they find it entertaining  to see how far they can push each other... I have no doubt he will get drunk no matter what he promises me...

Does this make me a bad person for worrying or just a spoil-sport... Does it make me bad that I think so poorly of his ability to rise above peer pressure? Should I just try to take his word for it and only be concerned if something does happen?

I'm just so confused...