Stats are useful tools for what they tell you, but they don’t necessarily tell you the answer to the question you have.
For instance, looking at divorce rates you can compare the number of divorces per year vs the number of marriages per year and get some comparison, but that doesn’t necessarily tell you a statistic about monogamy.
As mentioned, many marriages fail at being monogamous, which is often part of what leads to the divorce. Furthermore, the stigma of not being married has dropped significantly, leading to more couples entering long term stable romantic relationships but not getting married. And the effect of people who marry and divorce numerous times vs the number of people with one lifetime marriage and no divorces, or two marriages due to death of a first spouse.
And then there are gay couples, where marriage has only recently become an option, and is not a universally available one. Where do homosexual relationships fit into the question of “monogamy”?
It is fair to say that humans (as opposed to other apes like chimpanzees) are prone to form long term pair bonds. It is also fair to point out that the social structures and pressures that surround marriage do not always maintain sexual/romantic restriction one partner. And I’m not really talking about open marriages or poly arrangements, but good old-fashioned cheating. (Or not so good - YMMV.)
Another observation is that human pair-bond drives may not be lifelong, but have a lifespan. I have seen one estimate of 7 years. That would account for the male getting coupled long enough to help through the years of infancy but then fade as the children become more self-sufficient. In a hunter-gatherer society, 7 year olds would be able to contribute at some level and not be fully dependent upon their parents. And human societies as tribal groups would provide communal parenting options. I know, that has the obvious flaw that families aren’t limited to one child or one child every 7 years, so there’s a weakness in that argument.
What does any of this have to say about monogamy? That it never was as solid as we humans made it out to be? That the definition of monogamy itself has to be stretched to serial monogamy for it to have relevance?
And separately, the question can be asked if marriage is still useful or obsolete, or if the concept of marriage should be opened to include wider arrangements to remain relevant for the future.