The smell comes from ketones, both in diabetics, and during alcohol consumption in some people. Is your husband Asian, by any chance? They tend to lack a certain enzyme, causing alcohol to be metabolized differently (and making them feel as if they are taking 'antabuse'). I don't remember all of the different metabolic pathways offhand, but the smell alone doesn't mean he is an alcoholic-- other than telling you that he is drinking quite often.
Hello,
OK this is going to sound weird and I AM NOT a medical professional of any kind. However, my lhasa apso dog had diabetes and the way that the vet was able to tell (before blood work, etc.) is because her breath had what he described as the "sickly sweet odor" indicative of diabetes. Now, since a dog has fur covering the skin, I'd imagine the sickly sweet odor would on only be on the breath. A person, however, would emit the odor from their pores.
Anyway. Probably just a crazy thought but wanted to put it out there as a possibility.
Good luck!