A few years ago, I watched a lecture by Andrey Kurpatov in which he offered one explanation for today’s relationship problems that still resonates with me whenever I think about it.
He said that in almost all animal species, females choose males to reproduce with, and this is why males of most species are more colourful, have a more attractive appearance (not just a stronger physique), etc. Females are generally smaller, have duller colours, etc. For many years, humans followed a different dynamic: men had priority in choosing partners because marriages were formed mostly out of necessity, with men being the main providers. In modern times, this dynamic has almost reversed because there is practically no scarcity of basic necessities for women, and marriage is no longer a survival strategy. This makes old natural dynamics relevant again, and societies will need some time to adapt, provided nothing of global importance happens in the near future, such as major wars that could result in a significant reduction in the number of men.
In short, it’s a centuries-old conflict between natural instincts and established socio-psychological norms. I’d also add something of my own: primates, including humans, are not necessarily strictly monogamous by nature. Considering our evolutionary background, the abundance of modern options, constant stimuli to seek alternative partners, and how technology has made finding potential partners easier than ever, it’s hardly surprising that so many relationships intended to last a lifetime fail. To make matters more interesting, most of these options will never actually materialise, creating another problem: the paradox of choice, reminiscent of Buridan’s donkey, which starves between two equally tempting piles of hay.