I used to smoke, for 18 years off and on (!). I quit 3 years ago and I really can't see myself ever wanting to smoke again. In one day I literally stopped smoking and joined a gym, and decided to eat mega-healthy. It did help that at the time I was looking after a friend's house and dog, in a city where I knew hardly anyone and nowhere to go besides the nearby beach or the gym! So all I did was walk the dog along the beach first thing in the morning, come back and have a light breakfast, go to the gym and work out as much as I could, then come back and have a mega healthy big shake with lots of fresh fruit and soy yoghurt. Then it was dog walk time again etc.I felt more active and healthy than I'd had in a long time. Just to make sure, I lit one cig once, to see how it had affected me. Feeling that poisonous smoke go down my throat into my lungs and tasting the godawful taste of it really made me throw up in disgust - and I've never touched a cigarette since.
If that doesn't help, look at it from an ethical vegan point of view: tobacco is still being tested on animals, so by no means vegan. As if that wasn't enough, it is grown using shedloads of pesticides that kills even more animals, not to mention everything else that's alive in its tracks. The people who grow it, do so for a pittance - no tobacco is grown ethically, there is no "fair trade" tobacco, it all involves slave labour and at great cost to their own health.
And as for your own health; you will know what kind of diseases are related to smoking. Should you end up suffering from one - and I really hope you won't! - you will be subjected to all sorts of treatment and medication that, again, has been tested on animals.
Hope that will give you encouragement to stop smoking. Please do, it's great being a non-smoker!!
Let us know how you get on!