Please stay away from decent people, decent people have had enough of you, male and females.
I don't think we can easily separate the world into "decent" and "indecent" or good and bad people.
Most people in my experience, including those who have cheated on a partner at some point, or had a relationship with someone who was married/partnered, have aspects to their character that are decent, and exist in the grey area where they have both good and bad traits and do both good and bad things. They are not usually totally evil, or immoral. Of course, if you go to the pathological end, serial cheaters, scammers and liars who have no remorse, sociopaths/psychopaths/NPD, some are, but IME they're rare.
Traits that cheaters, and affair partners IME often do share is that they are weak willed, lack self discipline and resilience, and often believe themselves to be more hard done by in life than they are. This means they're more likely to think in a way that can justify an affair "my life is so rubbish, I deserve a bit of happiness and fun" kind of thing. They are often the kinds of people who have had easy, pampered lives, or been a bit spoiled, and find family life and responsibilities constraining and dull, and are inclined to feel disappointed with life. Or, they have grown up in dysfunction and don't know what a "normal" family life is like. If your home growing up was unpredictable and full of drama, a stable, normal family life can feel unsettling, like you are just waiting for the other shoe to drop. The unpredictability and excitement of an illicit affair feels familiar and sort of comforting to them. The latter group are easier to work with therapeutically to help them gain insight and change patterns.
I think there is probably more cheating, divorce, and more of this poly/non-monogamy nonsense, in the modern world because our lives in some ways are far too easy and in the age of Amazon, we don't have to learn to delay gratification so much, or curb our impulses towards meanness, sleaziness or dishonesty, when we can hide behind anonymity on a screen, and hide our actions behind fingerprints and pass codes on devices.
We also have to beware the black and white thinking that leads us to see victims of cheating as 100% blameless, innocent and all good, while the cheater is all bad. Victims, too, exist in that same grey area where they have both good and bad aspects to their character, as we all do. Being a victim of something bad also does not excuse or justify any kind of behaviour afterwards. There has been many a time where I have had to have hard conversations with a partner who wants to stay, but their behaviour clearly shows they cannot cope with it, and that can turn into a very toxic or even abusive dynamic.