I stumbled across an eye opening article about a year ago:

http://polyamorydiaries.com/why-men-cheat/
It is wonderful and should be read by everyone. Even those that have no intention of breaking away from monogamy.

This path lead me to read the book "Sex at Dawn" by Christopher Ryan.
That's a great read as well! It touches on the evolution of our species and how our psychology and physiology is geared towards polyamory. Agriculture and private property is what changed our environment to make it economically beneficial to move towards a culture that encourages monogamy.
The economics behind the paleolithic period is explained very well by Hans-Hermann Hoppe in this (free!) book:
https://mises.org/library/short-history-man-progress-and-decline
Highly recommend you nerd out on this one!

Everyone trying to live a happy life should UNDERSTAND these concepts since otherwise you will fall into a bunch of mental traps including this infamous false dichotomy.
When someone is cheating people often say:

1. You should stop craving sexual novelty. You are bad for thinking about other men/women.
2. Be a man(or woman) and break it off. And find someone else... (with whom you'll end up doing the same thing - craving novelty)

People actually give advice that equates to: "ignore your feelings and thoughts and throw away the most important relationship of your life"
Yes.. give up on your best friend, the mother/father of your children, the person with whom you have a mortgage, the person knows you better than everyone else. All because you are hardwired to crave novelty.

There's also the zero sum game that's assumed with relationships.
You can have multiple friends that each have their own flavor/spice. A person with whom you party with, another with whom you go hiking with, another friend to have deep discussions with, etc. None of these friends take away love from the others.
This logic is not applied to someone with whom you have sex with though.
Relationships are not black and white, there are infinite shades of grey. There are infinite ways to set up a life with other humans. Some people are monogamous, some dig orgies, some have a main spouse with a few friends with benefits, some go out hunting WITH their spouse, etc.

I think this is the next logical step for western cultural evolution. To understand our biology, then design a lifestyle that takes this into consideration in order to maximize happiness and avoid the far to often depression associated with modern culture.