To be a bit controversial, I disagree with those who say he will realise, he will want to come back, he will regret what he's done. In my (limited) experience, men who can't handle not being the centre of attention don't spend time realising, wanting, regretting. They do what they do, and either they look at, but don't care about, the devastation they leave in their wake or they just don't look. And if they don't look, it's either because they can't face the reality of what they have done or because they simply aren't the sort of people who think about, and take responsibility for, their own actions.
I had one of them, he left after a long marriage for a younger woman he worked with, because he didn't feel important at home, I didn't want what he wanted, he'd changed etc etc. I didn't feel important either, but that's by the by. As in your case, the decision was made long before I was told of it, and (in my case at least) it was compounded by untruths. He has since married the OW, so I can only assume he did the right thing for him. He was not confused, just determined to go, and to be with OW
I wanted to try to repair our relationship and I wasn't given the chance. In the end, maybe that was a blessing, as I didn't have the confusion you are experiencing, but it does sound like he's doing a good job of blaming you (and you didn't encourage him to chat someone else up or shag her, so whatever what wrong, he can't say he's tried to repair it).
My life in the last 4 years has changed considerably, and vastly for the better. Everyone says it will, and that time will help, I certainly didn't see that it would, or could, but it is true: maybe you can't see it, but there is a light at the end of the tunnel. Life will be ok, but it will also be different from how you imagined it. I'd just say, take time to decide what YOU want, because you are important in this. From what you've said, it seems to me that he is emphatically not good enough for you.