Confused

I know how to respond to an addict ~ tough love, no money etc.  But how does one react to someone that has both a fragile mental illness and alcoholism?  I find myself being so much more careful and nervous on the inside but outwardly I am respond to my son as if he were just an alcoholic.  He's not happy with me.  
For instance - he asked if he could work around the house to earn some money so that he could buy his friend a birthday gift, some food (he told me offered to cook, too, at the cook-out party) and cigarettes.  Well, I told him he could and he worked hard and fast.  He did a lot.  Then a voice in my brain heard what he always says to me "Mom, I couldn't drink because I don't have any money".  So then I offer to go with him to the grocery to buy what he needs (I had already bought him smokes) and he said no.  He said that I didn't follow through on our agreement and that I'm trying to control him.  So he wasn't about to beg me and then asked my husband for money.  After reflecting on what he said, I know he is right.  I should have followed through.  He said he'll drink anyway but he's very "careful".  Whatever.  I need to figure out how to relate to him.  This one isn't as clear.  Or maybe it is?