Its this morality thing again, someone somewhere decided for everyone how a marraige or in general life SHOULD be and taught everyone else a very narrow definition of how we should do things. It would seem(from experience, my own and every family I know, every friend who has the same stories) that MOST people can't follow this supposedly ideal life which is get married, be happy, never be with anyone else.... but why?
Can someone explain why we can't find someone we enjoy spending time with... and also enjoy spending time with other people. You can find your perfect life partner, but still be attracted to other women and want to have sex with them, but come back and have sex, talk, have kids and go bowling with the woman who you spend most of your time with?
Why cling yourself to one person, insist the only way you can "love" that person is denying any and all new connections with other people. Some people will do that, will only ever enjoy being with their wife, won't be tempted, thats fine. Many other people will get bored, cheat, lie, and break up under bad terms all because you agreed to something there was no need to agree to in the first place.
Its essentially a game of expectations, if you get together with someone and pretend that its normal to find someone and never want any change in your life, then if/when that change happens you get disappointed and usually angry. If people simply got together with the HOPE they might be together forever, but the expecation they will enjoy anything from a short to very long time together but are likely to drift apart, then if/when it happens its not a huge deal. You decide to move apart on a friendly basis, stay friends.
Kids don't get messed up by parents splitting, but HOW they split and how they act afterwards, divorced parents who argue and can't be in the same room generally end up crap parents, sensible people who move apart, divorce but are fine tend to have little to no problem with their kids.
Should you dip your wick in someone else, not if you've made a promise you won't to your other half. Its wrong to agree to do something and then cheat, its sensible to not make the agreement in the first place.
Women are essentially asking for this to happen by pretending their goal in life is to be married, often "encourage" their partners into commitment, rather than just be happy together till you don't want to be together anymore.
Women know, absolutely KNOW that most marraiges don't work, that a huge portion if not the majority of men and women cheat, yet insist on getting married.
Marraige is stupidly flawed, you can't possibly know how you'll feel about someone next year, let alone 10 or 50 years from now, making unrealistic expectations hurts everyone, frequently, for no reason at all.