Are monoamorous relationships natural?
Well, who cares? No, really. Why should we care any more what is deemed to be “natural” in humans? In the majority of cases, those things are no longer relevant in contemporary society, given how far humans have progressed from their “natural” state. For example, it’s “natural” for us to squat when we go to the toilet, but virtually nobody does that any more. In contrast, there’s nothing natural about using your mobile phone. So who cares if monoamorous relationships are natural? If you want one, that’s great. If you don’t want one, try and find someone who is accepting of that to be in a relationship with. But don’t use nature as an excuse for your actions.