there is usually quite a gap from the first time a person admits that drinking is a problem and then actually taking action. unless he had headphones on during the meeting, he probably heard SOMETHING that resonated - and that can actually scare the hell out of people. addiction doesn't dig threats much.....and will fight back tooth and nail.
as it is you've ONLY been dating for six months. and this guy comes with a whole set of luggage, plus a couple heavy footlockers. even if this brief attempt at sobriety sticks.....its going to become a really BIG DEAL for him. right now drinking is the center of his life....kind of like the Sun is the center of our little galaxy....and without it the whole thing falls apart.....for the addict/alcoholic a HUGE part of recovery is finding a new healthy long-lived center and then learn how to function in the new orbit.
its up to you if you want to be a small moon going along for the ride........