Is it unreasonable for me to prohibit my boyfriend from ever even trying smoking?

I told my boyfriend, that if he ever even tried smoking in the slightest, I'll break up with him. First of all my boyfriend has never expressed a desire to smoke at all, we were just talking about boundaries. A little background, my dad smoked throughout my entire childhood in the evening/nighttime while he worked, and I woke up coughing some nighs because of it, since his study was right below my room.
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Okay, prohibit was not the best word to use, but English is not my first language. I didn't prohibit him, I was just setting boundaries for if he wants to be with me. He is just as against it as I am, he just probably wouldn't break up over it, since he doesn't have the same past experiences with it as I have.
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Another update: mostly I think another reason I find it to be a dealbreaker for me for him to smoke, is that he is already very against it, so personality wise it would require a huge flip.
Is it unreasonable for me to prohibit my boyfriend from ever even trying smoking?
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