[spicoli]

I just read this entire thread...I think your answer lies in this:
Take the drugs out of the equation, for argument's sake, and let's pretend that we're talking about money. Every time you have money, you share it with your friend. You buy food, pay for movies, entertainment, etc...When he has money, he spends it all on himself, pays for his own food, clothes, entertainment, etc...Selfish? Yeah, a little. But it's his choice to spend his money where he wants/needs. Your choice to be generous with your money is your choice.
Never give anything with the expectation of getting it back or a favor being returned. Especially with friends and family.
It stops being generosity and giving when you are expecting anything in return.