That's not to say that some women don't have affairs just for the sex or that sex wasn't important.
56% of men who had affairs were happy in their marriage.
The theory that adultery is "natural" for men, fulfilling their Darwinian need to spread their seed, has been around a long time.
"She might even have an extra child to create more genetic variety in her lineage; if some children die, others will live on." That theory is controversial and can’t be proven or disproven eons later.
But experts say that women's motivations to have affairs are typically more than sexual.
After a business trip with a friend turned romantic, she began a long-term affair, a path she admits she was likely on anyway as her marriage dissolved.
Using another partner to transition out of a bad marriage is one of the common reasons women have affairs.
There are many reasons for infidelity such as revenge, boredom, the thrill of sexual novelty, sexual addiction.
But experts say that a large majority of the time, motivations differ by gender, with men searching for more sex or attention and women looking to fill an emotional void.
"Women tend to be more unhappy with the relationship they are in," Fisher says, "while men can be a lot happier in their primary relationship and also cheat.