My A has a spending problem, as well. The guess is it links back to his childhood - he still resents his parents' "You can have a baseball glove or we'll take you to the circus, but not both" - while his father golfed every weekend and certainly had more than enough for his booze.
Nonetheless, I'm actually grateful he's in inpatient rehab for the drinking right now, partly because of all the money we're saving! Since he's been in, he was planning on spending about $1200 on various dinner and lunches and items for the apartment... Since I'm in charge of the finances, our total bill for that time frame has been $73, and half of that was a full tank of gas.
I don't really know what to do about his spending, but I do know that it has been stressing me out much longer than the alcohol has.