I wonder if he is looking for someone "out there" to fill up the emptyness inside of him. This is what I have found with people who break up and then quickly get into a new relationship. I think for a long relationship like yours a one year hiatus from relationships is reasonable. Even if he broke things off, he still needs to "grieve" the loss which it doesn't look like he's doing. So he will repeat the same mistakes he made in the previous relationship.
I am glad you have gained some insight and now see that he didn't treat you as well as he could have.