Ophelia, I do think you have good cause to say to please do not ask again. If he has moved onto drugs, it will burn though whatever money he does have, and that is good cause to make it clear, up front, that you cannot and will not give him any money. I also think it's worth saying that it's a really bad idea to comingle funds with family members.
Hugs to you. Come vent out your frustrations anytime!