Make some rules for your friends.

My friends and I will give each other weed without charge because we don't mind giving it out when we have it and each of us gives each other weed. What's mine is theirs and what's theirs is mine... if it's available. If not then we don't bug each other about it... as we don't really NEED weed like some people do.

Tell your friends that if they want to smoke your weed, they gotta tone it down. How much they are smoking and how often, if they want more then they pay and don't expect them to pay you later, because obviously your friends think it's free. Tell 'em it's not. If they don't tone it down then tell them that it costs fucking money to be smoking all the time and that if you wanna smoke you gotta pay, either that or pay even MORE getting their own weed.

I don't know what else to say... your friends don't sound very cool.