changing yourself is not an act of love for her. It's a change for yourself. Nothing more. Nothing less.

If she was a platonic friend, would you quit...if all the feelings of love, except sex, still were still there? It still sounds to me like she'll withhold unless you quit. Your letting yoursellf be blackmailed.

At very least make it negotiable. Make her quit something you hate in return...junk food?? TV??? Shopping sprees?? Chewing her hair or nails??? I know there's something. I'd be surprised if you didn't find something more "unhealthy" in her as your smoking is.