If my boyfriend smoked, I would give him greif. Everyone knows what it does to people but i've lost my dad due to it, he died not long after my 12th birthday. I've went through my teen's without my father, and it's the worst thing that has ever happened to me. He smoked from the age of 14 and carried on until it eventually killed him.
I wouldn't date a smoker, ever. It's the most disgusting habit in the world and I wouldn't put up with it, no matter who did it. Your girlfriend gives you greif because she cares, it might be annoying but you and your health is important to her. It doesn't matter how much you smoke either, you are doing damage with every cigarette you smoke. At the end of the day, it's your decision, she is only trying to look out for you.