This and also it’s pretty selfish to keep a relationship going only because maybe they’ll change in a way that suits your needs better. I also don’t think it’s ever good for a person to change only for someone else’s approval, you have to really want it for yourself. I would definitely talk to him about it. It might even help to outright start the convo with “I don’t want you to feel like I’m attacking you, bc that’s not my intention.” It lays a bit of groundwork before getting into it.
I also think he may take it as a bit hypocritical, which is a valid viewpoint. But I also understand where you’re coming from OP. I used to smoke 6-8 blunts A DAY, on average. I could not have continued college that way. When I graduated I was still smoking daily but only 1-2 little bubbler bowls, so SIGNIFICANTLY less. It made a huge impact on my health physically and mentally, which I rolled my eyes at the idea of until actually slowing myself down and realizing the difference.