litphoria

A character that is in a romantic relationship with more than one person, and all partners are aware of the arrangement.

Okay, but, like... either we go for Monogamous and Polygamous or for Monoamorous and Polyamorous - we shouldn't mix them like this. Especially since currently suggested description for Monogamous doesn't point out any kind of formal relation either.

Not to be mean, but my Brit dictionary for FF says that 'polyamorous' is not a good word and suggests 'polygamous' as a valid way to say that so... yeah, dictionary battles won't take us far this time. I just want some consistency in how the things are handled. Because right now it sounds like Polygamous would be valid another thing because of technicality and we want them not to be needlessly specific, yes?
I get the distinction between Open and Polygamous, but Polygamous and Polyamorous is very similar and if we want to have Monogamous, we should, for consistency, have Polygamous. Neither of them are defined by formally or religiously 'valid' relations either way.

No, it means I actually don't see the use - which make this part:

Polygamy is 'many spouses' whereas polyamory is just 'many loves'. They're almost the same, in the way that 'long-term relationship' is almost the same as 'marriage.'

Not make sense for me. If we understand Monogamy as "romantic relationship with only one person" why would we suddenly not understand Polygamy as "romantic relationship with more than one person, and all partners are aware of the arrangement", but try to put spouses there?
And yes, I am arguing semantics here - I think the alternatives should be named within same convention. Thus, just have Polygamous to fit the Monogamous.

Polygamy is very specifically having more than one spouse, not just more than one romantic partner.

Monogamy is the same, at least in Oxford dictionary. And both Monogamy and Polygamy have described applications in relation to animals., which you referenced before.
Plus, 'Polygamy' is wider-known term than 'Polyamory' or however it should be named. Especially for non-native speakers. I literally had to have a trip around Google just to make sure this is not putting in some internet made-up word.

Polyamory and Polyamorous have become widely used and accepted terms in the kink community, notably on websites such as Fetlife. I think this is because it denotes "Many loves" without the assumption of "Many marriage relationships" which has much wider application in that community. Also that in every state, polygamy is defined as a crime, where polyamory is not, and many one Fetlife, who are describing their actual living situation, would not want to publish on the internet that they are guilty of a crime. I am not endorsing either way, just telling you what I have observed.

Monagamy

Monogamy does have a wider meaning due to being applied in biology, whereas Polygamy is only applied to marriage, not the non-monogamous behavior of various species. Thus, people who are not married would say that they are in a monogamous relationship. That said, there is no reason not to have both Polygamy to express a marriage relationship, and Polyamorous to indicate a non-marriage relationship. Polygamy definitely needs to be added, but it is not an alternative meaning of Polyamorous. Presumably, a husband with a mistress would select Polyamorous Relationship and not Polygamous Relationship. A faithful husband married to two women would choose Polygamous, though Polyamorous would work still generally work for him if Polygamy is not a choice.