Boyfriend trouble😪

My boyfriend and I are going into our senior year of high school and have been dating for almost 2 years. He's my best friend and I love him so much. So long story short, he was always super well behaved and was never into drugs or alcohol or things like that. But lately, he's smoked weed with his friend and they vape together a lot. I think it's really really really stupid. I know he's going through a little rebellious phase because he has super strict parents, but it just gets on my nerves. If I ever did anything he really didn't approve of, I'm sure I'd never hear the end of it. I want to talk to him, but I don't even know how to approach the topic. What should I do??