Welcome to SR, Kt54. I'm sorry you are going through this. Unfortunately, what has happened to you isn't unusual. Often, the addict will find it easier to move on to someone new, who doesn't know about their addictions. Someone they can hide these things from for a while, like he did with you, at first. But, it's hard to keep up that facade for long. As with you, he finally admitted his alcoholism. Now you know, and he may feel like he can't truly be himself, which includes drinking. Addicts just naturally try to find the easiest way to continue using/drinking.
It doesn't mean he didn't care for you or lied about his feelings for you. If he has moved on, it really has nothing at all to do with you. What it does mean is that he is not ready to quit drinking, and rather than face you with the truth, he is distancing himself.