my fiance is a heavy machinery operator and he gets stressed a lot so he smokes once in a while. I'm…

my fiance is a heavy machinery operator and he gets stressed a lot so he smokes once in a while. I'm fine with that as long as he doesn't make a habit of it. what bothers me is he knows I hate the smell but he'll do it right before he comes home and then lies about it and tries to cover it up with gum :( I think I'm over reacting but it just bothers me he feels he has to lie