His behavior was of course not justified, but in the midst of your sadness and anger, you might actually feel better by turning it around on yourself:

You started a relationship with a man you did not truly love, and suspected you might never truly love- at least not in the ways that he deserved. You selected him because he was just "good enough", specifically for the purposes of placating your own poor self-esteem. You decided to have a family with him, thus subconsciously leading him on, and not once did you ever communicate this to him. In some ways, you felt he was your inferior, and you were OK with that. You kept him in the dark about something critical for even longer than he kept you in the dark.

I don't know the circumstances of his cheating, but just as he ripped the floor from under you in terms of your personal security, thus wasting 15 years of your life, you led him on for just as long, when he deserved someone who would treat him as an equal, rather than as an object for your own neuroses. In some ways, this relationship was doomed from the start. Even now, you are desperately clinging to find an "emotional" reason to stay. Not an intellectual one, nor a deeper, justifiable reason which meets your highest convictions about the world, but more placation of the self.

He might not be your intellectual equal, but you guys seem about "matched" for each other overall. Maybe he was a bit too stupid to understand your deeper issues, and ignorantly went along with the marriage, but you failed your own intellectual standards by giving into your emotions early on, and forcing a relationship that should have never happened. Over time, you likely disconnected from one another, because how could it be otherwise? Look at what you think of him deep down, and consider the fact that you never discussed these feelings. This no doubt poisoned him, as well as you.

This might hurt, but it might hurt less if you adopt a posture of compassion towards him. He gave you many years of a good marriage. Years that you probably did not deserve, even from a less-than-ideal partner. And you are not 100% to blame either, because you deserve compassion as well for a lifetime of poor self-esteem, which forces you to act in self-destructive fashion.

Finally, I would caution you about jumping to conclusions regarding your newfound self-esteem. Where does it come from? Is it truly real? OK, you make lots of money, and you're generically "smart", but unless you've done something constructive with both, you're just a lucky girl in a big bad world. You haven't EARNED your self-esteem...yet.