Humans have a sexual ration close to 1:1, thus we cannot practice polygamy, unless you want herds of outcast males as other species have. Human society is only stable with faithful monogamy, be that lifelong or serial, it doesn't matter which so long as we keep to one romantic partner each.
Habitual keeping of more than one sexual partner, be it spouse and/or lovers, to my heart and soul, is polygamy and a form of emotional cowardice.
Polygamy is living in a room full of candy because you are terrified of starvation, yet in doing so you lose all appreciation for food or the effort it takes to grow and prepare a good meal. As such, it is a form of greed, a vice. Just some advice. Take it or leave it.
Polyamorous and polygamy, if we leave the semantic level and enter the level of emotional reality, are the same thing. Perhaps one has a lower risk of sexual disease than the other, but it's all the same shit.
The pain of losing a monogamous partner is so extreme that the damage of heartbreak can be seen on brain scans. So, polyamorous, polygamous, cheating types, you avoid this damage because you spread your emotional bonds more thinly. Yet in lowering the curse you lower the blessing too. And, I tell you this, the secret of immortality is in monogamy, for heaven needs emotional bravery not cowardice, needs true loving pairs not emotional parasites who spread the pain that should be rightfully theirs onto the backs of many vulnerable others.