There is a quote from the AA Big Book I see posted a lot, usually to another alcholic who has posted the idea of drinking moderately. It reads in part:
The idea that somehow, someday he will control and enjoy his drinking is the great obsession of every abnormal drinker.
Your husband may have never shaken the idea that one day he can drink.
There are a lot of bumps in recovery. Some lead to relapses. I'm more worried about my own "stinking thinking" leading me back to the bottle. Alcohol is cunning and baffling. The lure to drink is unknowable to the non-drinker. But a recovery program should be helping him with this. Is he in one? Abstinence is not recovery. Abstinence is just a long wait for the next drink.
Good luck to you, and to your husband.