if he has all his shit in order then let him do what he wants to do. it doesnt seem like the issue is pot, it seems like the issue is about your relationship. you obviously have a didnt idea of what a friendship is compared to him. express your feelings and see where it takes you guys.
now realistically...YOUR BOTH GUYS, now continue being guys and forget about spacing on picking up a dvd...and this poor memory thing. as long as he remembers he likes women and knows how to remove a cap or pull a tab then everything is fine.