Are you sure he's still not drinking since you don't live together?
It is hard to believe he can put up that front for 90 days. Maybe going to meetings puts him in a good mood. I'm home with my kids all day and when I go to an alanon meeting I''m so happy to be with people who've walked the same path. Could it be he's an extrovert and just gets excited when he's in the group? Anyone can be cheery for a couple hours, he might be having a harder time when he's alone.