Thank you for your question.
He could just be trying to figure things out as you suggest; but more than likely he is trying as he said to work it out with his ex. I believe, from what you are saying that his level of caring is low, else he would have called you while you were having the operation.
I do not believe he was using you to boost his self esteem. One might think that. But what I am seeing in what you wrote is that he really was confused. His wife had an affair and so he may have felt entitled or confused. Kind of like: well if she does not care anymore for me than that, I am free.
but once he tasted the freedom, and started thinking about his kids, his heart suddenly belongs there.
I do not think this reflects negatively on you, it is just something that is not where you would like it to be right now.
I definitely do not thing you are cheap or naive. It is hard to see the reality of a situation when you are so closed to it and so emotionally involved. It sometimes takes an outsider, like us, to see the truth.
My advise would be to let him go, and if he returns, to not start up again if he has not terminated the other relationship. He is just not available to you at the moment.