I think it depends on his and your drinking situation. I assume since you quit drinking you are in recovery? Does he have a drinking problem? Are you enabling him? Is it jeopardizing your sobriety? The answers to those questions would change my opinion 180 degrees. One end of the spectrum I could say it's no different than asking your significant other to make your favorite food. The opposite answer I would have depending on your answers to the questions I asked would be "hell no don't buy him booze"