I'm a big fan of the Art of Manliness blog - lots of good writing, ideas, and useful info for guys. In their very well written Man Killer Series ( Money, power, and sex ) I found the best, most consice reasoning behind why men cheat:
"Neuman explains that the feeling of being underappreciated (emphasis added) is the most common emotional factor among cheating men. Somewhere in the midst of diaper changes and mortgage payments life tends to beat the gratefulness out of marriages. Couples that once wrote poems of each other’s beauty and worthiness now suddenly can’t muster up the strength to say thank you. And it hits men at the core."
Oh, and just so you know, 48% of cheating men say that is emotional dissatisfaction that lead to the straying ways. The yearning for appreciation is strong one for men. We search for it from our bosses, our loved ones, our direct reports, our kids, the media - everywhere.
That is why we get choked up at the final scene of Gladiator, when they carry Maximus off and leave Commodus on the sandy floor of the Colliseum. Rome is showing her appreciation of the man. Watching that happen, especially to a troubled, noble, and virtuous man, well.... We all hope to gain some of that in life.
Kate and I finish every day with 3 Happies and 1 Appreciation. It is our way of making "thank you's" a habit. It's one of my favorite parts of the day and I've been known to wake her up to hear those words.
Want to keep your man engaged? Figure out how you can make him feel appreciated, needed, and useful. Then, make sure to let him know. Daily. (Check out this book for ideas on finding out how he feels appreciated. It's the best I've read on the subject.)