"Monogamy is not really working but perhaps serial monogamy could be doable for the most part"?
This seems to imply that the top reason why married people divorce or cheat is because they're "tired" of having sex with one person.
In some instances that may be true but for the most part I believe there are a variety of reasons why people step out on their marriages.
Note: Most cheaters have no desire to (replace) one relationship with another one! Their goal is to "compliment" what they already have.
To cheat means to "break the rules" using secrecy, lies, and deception. Some people cheat for the thrill of being sneaky.
Based upon my observation cheaters tend to be looking to hold onto all that is "good" in their primary relationship while addressing their other "needs" on the side whatever those may be.
In other words they don't actually want out!
A few years ago an article was written stating the "7 year itch" is now the "3 year itch". "67 percent of couples say that habits of their partner that they once considered endearing or harmless become major turn-offs by the three-year mark."
Another major complaint couples have is they feel their mate "changed". It's almost a cliché to hear someone say:
"He/she is not the same person I fell in love with."
Essentially a lot of folks gradually STOP doing the things that won their mate's heart. Maybe it's human nature to "relax", "slack off", "put in less effort", or take people for granted when you believe they won't leave you. They don't realize it's the "work" that provides the "security" in marriages not the vows or marriage license.
Not long ago I saw a comment from a woman on HP who stated she couldn't wait to be done with the "whole dating thing" always having to look her best, watching what she said and did. "Once you're married it is what it is!" My guess is she is not the only person who views marriage as a time for "relaxing" and not being as concerned about their mates likes or dislikes.
It's possible that a 5 year or 10 year contract might motivate some people keep up their efforts to maintain a quality relationship if they knew a contract was coming to an end. Then again you might see a rash of people only making the effort when it got within 6 months of a decision to renew. :)
The bottom line is people don't cheat because they want out.
Divorce has always been an available option.
In fact many might claim they cheat in order to tolerate their marriage.
Whatever they may be "unhappy" with doesn't rise up to the level of going through a divorce, splitting up assets, lowering their living standard...etc
Ultimately contract or not there will always be people who cheat.