Husband has had a cigarette here and there

I know it might sound silly but I have always hated smoking the smell the health risks, the addiction and my husband has known this but every now and again ( as in he has had 2 since I have been pregnant in 5 months) he will have one cigarette usually when he hangs out with his siblings who are all smokers. I can't help but get so upset by this. I fear he will become a full smoker one-day like them but he sees that I over react and that he doesnt do it that often which is true but how can I stop feeling this way?