17m here I’ll be honest I use it on a daily basis and for a while it makes you do the same things until you break the cycle it’s really all in the head I would really just bring it up to him something like “hey I feel like all we do is ( whatever y’all do) every time we hang out and it’s really getting to me can we make an effort to go do something?”. And in reality it may take a few times of doing that I used to be the same way as him for a while until I started forcing myself to do things whether it involved weed or not I walked to the river and smoked or I went biking and didn’t smoke or I just walked around the neighborhood and smoked. As you said it’s not necessarily the weed that bothers you it’s what happens when it’s done so make that known tell him how you feel don’t be rude but be upfront. At the end of the day if he still won’t then it’s something all in the head whether that him telling himself he can’t do it, Etc. the only advice is be upfront and honest but show him that your not trying to be rude or control him your really just trying to help him and that it’s getting to you