Hi & welcome to SR!
I'm sorry you need to be here, but glad you found us.
I can understand that you're wondering how he could just walk away after a year. But you know, quite honestly, he's probably wondering the same thing.
To you, his drinking (as you've told him numerous times, no doubt) is a problem for you. To an addict, anything that interferes with his drinking is a problem. I can't tell you how quickly my ex moved on to finding a girlfriend who was OK with his drinking (until she wasn't anymore). And the next one. And the next one.
I found, with my ex, that what I really wanted when I left him wasn't for him to be broken and sad and miserable. I wanted him to acknowledge that we had had a very good thing and that HE had screwed it up by his drinking. I wanted him to admit that it was all his fault that things went south.
I never did get that. What I got was a whole lot of abuse heaped on me for "abandoning" him (as if he were a helpless puppy dog), for "violating" my marriage vows (because apparently I was supposed to put up with whatever he decided to dish out without complaining -- don't remember that in my vows...), for being a horrible lying [insert insults here], etc.
What I finally had to come to terms with was that it didn't really matter how he thought of me, or the 20-year marriage we had, or his own part in its demise. It also didn't matter what anyone else thought -- his friends who called me a bad Christian; his parents who never spoke to me again despite knowing he was an abusive alcoholic; etc. The only thing that mattered was that I knew that our marriage was breaking me down, and that since his choice was to continue drinking; my choice to save myself and the kids from that hell was completely and utterly valid and something I could stand by.
Getting validation from an active addict that their addiction and addiction--related behaviors have ANYTHING to do with the breakdown of a relationship... it's something you can wish for, but it's very rare that you'll actually get it. I had to provide my own closure -- and it took time for me to be OK with that.