You are right to know what you want and to walk away from a relationship that isn't what you're looking for. You are wrong to try to change someone to fit your expectations.
The challenge you will face is when you realize that no one is a perfect mate. To have an enduring relationship, you have to be able to accept something about your partner that is not ideal. The difficult choice is knowing where to draw that line. If smoking is where you draw that line, then more power to you, but I can think of a lot worse things to tolerate. It will depend on how motivated you are to find someone to be "official" with, and how many alternatives you think you have.
I don't smoke. However, I've had girlfriends who did, and while I didn't like it, that's not why we broke up, and that's not nearly the most difficult trait in a girlfriend that I've ever dealt with.
As to the posts about "dangerous/deadly/hazardous" etc., I think that some people sweat the small stuff too much. We'll all be dying of something, and we all do something that might arguably decrease our longevity (personally, I happen to LOVE potato chips, which might possibly be the worst thing you could eat!). Or you might live a model healthy lifestyle and get cancer anyway! If a relationship makes you happy, stick with it. No sense living to an old age just be miserable for a little longer.
And for those that "just have to be who they are", go ahead and be yourself. However, there should also be room for introspection in your life. Sometimes people who "call em' like they see em'" see things wrong and call them wrong. Being prepared to change something about yourself is a sign of strength and confidence, not weakness. Finding someone to share your life with is a negotiation. In any negotiation it's easy (and requires no talent) to say no. It usually takes a lot of creativity and talent to say yes.