One reason cheating is prevalent and the divorce rate is so high is because of settling down, especially now in our promiscuous society. This is true for both genders, but from what I read and observed its more prevalent in women. Because we live in a promiscuous society, people will experience a greater quantity of relationships. The more relationships your future partner has, the less likely you are their best relationship (except me i will always be the best), and there is a high chance that they will yearn for that one special relationship that didn't work out and never will work out, but they cling onto it. But since time is running out, they have to settle down and live a more stable life. So they will choose a partner that probably won't be as fulfilling to be with compared to that one relationship from the past. As a result, every fight and argument becomes magnified and the resentment slowly starts to build, which then eventually results in cheating and divorce. This is part of the reason why body count is important. Pre 1960s we had a more closed society with less promiscuity, so people had less relationships and sexual partners, which meant that you were statistically favored to be your partner's best relationship. Also many other factors (such as economic conditions) but not gonna list everything.
As a man, to minimize the chance of being cheated on, you have to make sure your woman finds you sexually attractive on a primal level (no money, assets etc.). Just from a primal standpoint. This comes from working out (strength and size), knowing how to fight and being imposing. In eastern Europe you will find many men who are not attractive at all married to some of the most beautiful women in the world, simply because they are imposing and brutish and there is an aspect of violence that exists with them. Not saying they beat their wives, they usually don't, but they have the capability of causing serious harm to people that threaten her, which is where that primal attraction comes from. Many men in western societies have become weak and frail and let the world push them around, of course their women will not respect them. These wives then yearn for their relationships of the past which were with men they found primally attractive, and so that resentment begins to grow. There are many other factors of course but for the sake of this post I will use generalizations.