Really there is no cookie cutter answer. Every relationship is different. Many men and women marry someone and 20 years later that is not the person they would have chosen to be with, the attraction is gone, the sex is gone or boring, they can’t even stand to be in the same room as the person anymore, but they take for granted what the person does for them, and when faced with the loss of it, and the home they bought together, and the ease that comes with a two person income, pension, not having to pay for a divorce, and the kids thinking well of you, they are freaked out and would rather keep their old life. This does NOT equate to love, and is extremely common, especially for men, so while your rose tinted spectacles view is nice, and no doubt true for some men, I’d say for many, they are having an affair with someone they actually do love and in an ideal world would much prefer to be with, but they are just cowards and when things go wrong, they want the material stuff and easy life more. The end of a marriage is a huge deal and can have a gigantic fallout. When my husband told me he loved me and didn’t want me to leave, I knew he was a liar, I knew it wasn’t ME, I was attractive, successful, and loved him, and did everything for him. It wasn’t about it whether I was deficient, I wasn’t, but we grew apart, we wouldn’t likely have chosen each other at 40 like we did at 20. His affair partner he showed love to that he didn’t show to me, I read the messages. They had something, end of, I’d be lying if I said they didn’t. He was fond of me, I was his family, he imagined getting old with me (while not having much sex and shagging other women) there were financial rewards and seeing the grandchildren and kids and being in the dream home we had bought and tons of other reasons. That wasn’t love for ME, that was love for himself-if allowed he would have liked to have it all, including his lover, but he was materialistic at heart and his reputation meant more to him than anything or anyone else. I didn’t believe the pleas and lies and broke up. 6 months later he was engaged to the other woman. They are very happy, it’s clear, and I am now happy too