"Historically" is a narrow term, we don't know much of our 50k years of history, or what we know of, societies handled this very creatively. Like how sleeping with outsiders was not a taboo due to needing new genetic material, or that childrens would be raised communally as parents might often die or not present to do other tasks. I don't see this inevitability of monogamy - my kitchen table theory is that the current state of >mostly monogamism< was driven by a globalising world (even 1-2k years ago) that favored imperialism, standardization, expansion, relied on the heavy physical labour while being very resource constrained. Religions placating chivalry and honor were a supporting policing tool.

All of the "classical sins" could be described as are human nature regardless of relationship type. Note that as an alternative I don't just think of flat hierarchy polyamory here, any non-heteronormative relationship or constellations that revolve around a "main relationship".

In a world of industry standards, automatization, light and flexible work hours, easy communication and high mobility I think we need to be creative again. Especially how this above evolution seems to reach its limits, and "scale to the moon" does not seem to work (dead internet) and we're in dire need of small, informal communities again. I see much more openness to this from the younger western generation.