To look at infidelity from the point of view of sex is a complete narrowing of the phenomenon. There's a reason that the commandment is repeated twice in the Bible - once for doing it and once for thinking about it. We have always created structures and broken structures. It is essential to the human spirit.
Esther PerelEven a good marriage leaves people with longings for certain things their marriage will never be. So, do they accept that, make compromises, and say, "You can't have everything in life," which is what we always did? Or do they say, "I deserve more. I want to experience that thing and, you know, I have fifty more years to live than I used to." It's not necessarily that we have more desires today, but we do feel more entitled to pursue them. We live in this "right to happiness" culture, and yes, we do live half a century longer than we used to.
Esther PerelIn dating, if you say no, your lover goes on to the next person. In marriage, if you say no, the person stays.
Esther Perel