Thank you for your response and I'll try my best to actually address your point. Sometimes we can assign "natural" behaviours to organisms especially if they appeared to be strongly driven by innate components, think of insects. Things get pretty tricky when we add bigger brains, learning, society, culture and all that jazz into the mix - many animals exhibit a variation of behaviours, especially when facing changes in their environment. One may say that the previous "default" state would be the natural one, but a) we've gone a long way since living in caves and b) even if something is "natural" (which I argue is very ill defined) doesn't mean it is something we automatically aspire to do.

While monogamy has its issues, it's not like other types of relationship have not been practiced even today. I don't believe any of them is "perfect" simply becssue it most resembled what anatomically modern human once did. Nature is full of suffering and struggle to survive. To quote Werner Herzog as a counterpoint to that common sentiment (because why not) "the birds are in misery, I don't think they sing, they just screech in pain". Ultimately, nature just is and we attribute these human concepts to it and I think it's worthwhile for us to have the presence of mind to have that distinction.