Would you break up with someone if they started to smoke?

When my fiancé and I first started dating, I told him how much I hated smokers. I lost many of my family members due to lung cancer and I just can't handle the smell of tobacco. He agreed and also told me that he wasn't attracted to smokers and could never be with someone who smokes. Well, fast forward two years and he is now a smoker. I didn't even find out until recently because he's deployed and we spend MONTHS apart from each other. I talked to him about it and he tells me that it's to "relieve stress" from work and school, but Idk how I feel about it. It's kind of a deal breaker for me, he knows this and I know that he's not just gonna quit cold turkey... Feeling indifferent. :(