Am I too possessive?

Hey, I'm an 18 year old girl and I'm in a relationship for about more than 2 years now. I really love my boyfriend and I couldn't imagine living without him. There's only this 1 thing, that makes me feel bad over & over again... Well, my boyfriend is the more 'experimental' type of guy. He really wants to try all types of things, especially drugs, and I'm not really okay with it. I don't mind if he smokes a joint every now & then, but he wants more... It makes me feel really bad, but when I talk to him about it, it's always the same thing. He says that he knows what he's doing and so on. I (want to) believe him, but this doesn't take away the 'bad' feeling about it. He says it's ridiculous, because I can't really say why I don't like it. "It's just a cliché anti-drug attitude, you need to get over it blablabla." Then we end up fighting. Every time again, I want to 'control' my emotions and not make a fuss about it, but I just can't stop myself from feeling bad about it... Sometimes he says that I 'suffocate' him and that I take away his youth, which makes me feel very guilty. I just want him to have a good time with his friends, I don't want to suffocate him. I'm so scared that this thing will come between us. One day it will be too much for one of us. I really can't manage to be 'okay with it' and control myself whenever he does it, but I don't want him to feel suffocated either. I really don't know what to do anymore.