My boyfriend smokes and it makes me uncomfortable

Here’s a little backstory and I want to explain first that I’m not against people smoking. I know a ton of people including my family who smokes and I know a lot of people don’t see it as a bad thing. But personally for me it has only ever caused negative impacts on my life and i just choose to not involve myself. I let my friends smoke around me. I never complain I really don’t care actually. But one thing I’ve always cared about it that I would never date anyone who smokes. I’ve been dating this boy since I was 13 and we both agreed smoking is stupid and that we would never do it and it made me very happy knowing I don’t have to worry about it. He understood it was stupid, wastes money, ruined your lungs, and overall I (I thought we both did) saw it as a scapegoat of social situations. Once again I’m not trying to bash on anyone this is my personal dating preference. We broke up for a little bit and his sisters boyfriend got him into smoking. We are now talking again and he has said that he only does it sometimes but I was so worried that he would waste money on it and invest himself into it. And he did. And now that we are talking every time I hear his sisters boyfriends name I’m filled with rage and when he’s over I know (or I just always feel) that they’re smoking. I hate it. Its a little crazy of me. And I wish I wasn’t like this but I am. We aren’t really dating yet, and that’s because he says he’s not ready, but when he is and if we start dating I don’t know if I can handle him smoking. And when he says he wont or isn’t I have a hard time trusting it. He was never like this before I never imagined him becoming like this. I do not know what to do. Please give me your advice. And I’m not asking to see the light in smoking, I want to know how to resolve my anxiety in this situation