You need to talk to him again and try to get it through his head! Maybe tell him to look it like this- say he kind of like cashews but really only eats them every couple months. But imagine he likes to dump a package of peanuts into the trail mix you keep on the table just in case he's hungry for them. Then imagine you have a deadly allergy to those peanuts! Explain that it's not a big deal to him but that booze is like the deadly peanuts to you.