It's very easy for us to fall into thinking that any temporary reduction in drinking, no matter how small or how transient, is significant. It's not. It's simply part of the cycle.
My ex's drinking used to follow a pattern. She'd start off not drinking much. More than the average person her age, but not much compared to what she typically drank. I'd be wary. Over a few weeks, her drinking would ramp up to a lot. I'd be cross and resentful and walking on eggshells. And then something really bad happened - a really nasty row with me or a friend/relation, her injuring herself while drunk, her turning up to pick up the kids from school while pissed etc - and then she'd stop. After the horrorshow of whatever it was that triggered that particular attempt at sobriety, I'd be overjoyed at seeing her stop drinking. And then a few days later she'd start again, not drinking much.
And so it goes on. All that's changed over the years is how quickly she progresses from one stage to the other (it used to be months; now it can be days), how bad she gets when she's really going for it (she used to be able to dry out on her own. Now she typically ends up in hospital) and how long she stays sober for in-between (used to be a day or so, now it can be months). But the cycle is still there.
I have no doubt that she justifies resuming drinking to herself in terms of being sure that, this time, she'll keep it under control. She's lying to herself of course but that's drug addictions for you. And if she convinces herself about her being able to keep it under control it's no surprise when she tells me exactly the same thing. I don't believe a word of it, but I can understand why she says it. She has to believe it because, if she didn't, she couldn't justify resuming drinking. If that sounds nuts that's because, well, it is. Drug addictions seriously mess with your head. I stopped smoking four or five years ago and have no intention of ever re-starting but I still get the occasional bonkers thoughts in my head about "Go on, just have a fag, you've had a hard day, you deserve it". WTF?
The best predictor of future behaviour is to observe past behaviour. If you have someone with a clear alcohol problem, and every time they have started drinking a little it sooner or later turns into a lot, you would have to have a hole in your head to imagine that it would be different next time.
But he doesn't have to stop. He could quite easily choose to continue drinking for the rest of his life while telling you whatever it is he thinks you need to hear to keep you hoping for him to change. Would that be good enough for you?