Is he smoking weed

To preface, i don’t date guys that drink, vape, or smoke weed due to some personal issues. I met my boyfriend a while ago and we’ve been dating for 7 months. So like he quit smoking right before he met me and my one rule is that he doesn’t do that shit and he recently admitted that he misses doing it and that all his friends do it. Ever since then we’ve fought over stupid things and I can’t help but worry he does it behind my back. What do I do? I don’t want to keep fighting.