In the context of a modern very long lifetime (by any historical standards), monogamy is a clearly a failure based on the simple statistic that most marriages fail by the 13th year -- a very small fraction of our adult lives! So after your first divorce, monogamy in the strict sense (of not counting serial) is no longer possible by definition.And, by the way, for many people, swinging or poly is an enhancement to their marriage, not a way to solve a problem.What seems to be happening is that each relationship of two or more, same or different genders, must have the "talk" and explore what the relationship must look like. And so when you are considering building any relationship, no matter how complex, keep in the forefront that you and your partner(s) must DESIGN the kind of relationship that works for all of you.And this involves a very serious discussion about sexual and emotional monogamy and non monogamy with NO prior assumptions. If monogamy isn't working (I dispute this claim somewhat), it is because people have become too self-involved, way too worried about their own "needs" etc. Positing poly relations as a a cure seems like putting out a fire with alcohol.
Longer life-spans, increasing independence for women, and relaxing sexual mores mean that many people in industrialized nations now prefer serial monogamy, in which people couple exclusively for a time before breaking up and then re-coupling exclusively with someone else.
Pooling the resources of multiple partners allows for more money, love, sex, and assistance for everyone, plus the added bonus of more sleep for families with infants.
Kids growing up with multiple adults caring for them get lots more attention and help with homework.
My wife and I have been swingers for 10 years, so I have more than a passing familiarity with this sort of thing, and have come into contact with pretty much all of its variations even if we choose to express our non-monogamy in only one way.
The saying in swinging is that its controlled by the women, which isn't exactly true, but women are often the lead in finding new couples, in large part because its less threatening than a man doing it.