I feel like my fiancé doesn’t want to grow up

This morning while looking for my car keys I found some weed that he had “stashed” away. He started a new job that can be dangerous and if he gets hurt, he has to pass a urine test to apply for workman’s comp. I don’t have an issue with weed itself, it’s just that it’s caused money issues in the past within our relationship and now he has a job that requires that he not smoke. I don’t know what to do. He always reassures me and tells me he’s stopped and then today I find his stash. I feel lied too and like I’m the only one in this relationship who wants to grow up.