People like to think of cheating as black and white; however, it isn't. There are so many greys and so many unique situations that couples find themselves in -- none of us can turn around and say, "I'd never do that," because we aren't that person living their life in their shoes.
Women are incredibly powerful to men. In fact, women are so powerful that it's overwhelming. Men need women to survive emotionally: our approval, our support and our encouragement, all of which enables them to flourish in the world. He idealized his wife so much that he felt small.
When I was younger, guys with cute dogs, hot cars and buff bodies were the ones with all the women. Today, average-looking men over 40 (without hot cars) need only say they're pained from a bad relationship, and it's as if a magic spell has been cast -- women come out of the woodwork.
Sadly, many men don't realize the profound effects infidelity can have on the emotional life of a trusting long-term partner. Inevitably, most cheaters are eventually found out, and the resulting fallout is often much greater than anticipated by the cheater.