I've been in this situation. And when it did turn around it was not because of anything I did, it was because HE sat down with himself and realized what he was doing and decided to change it.
I agree there most likely is something deep down that is going on with him, but he's the only one who can figure that out and he may or may not.
the only thing you can control is you.
I had reached the point where my trust was gone and I was okay with separating. I figured we'd still be in touch, and in each other's lives. It didn't come to that, but it came very close. I can tell you that if things hadn't changed i would have left and been okay with it at that point. My peace of mind was more important to me than dealing with the secrecy and lies.