This might be a silly question but is he taking any medication? For cravings, depression, anxiety, other illnesses etc?
I had a friend who's AH was on meds and had no issue with sex when he was actively drinking, but then when he started recovery they were having similar issues with lack of sex drive. The meds ended up being the issue for his lack of sex drive even though they were never changed. Alcohol does weird things when you are on medication.