To be honest, it is surprising that polyamory, with the woman taking in a multiman soup, works for anybody. If you want to play anthropologist for the day, the only societies that practice that, have reasons for it, and it is between two brothers. So the offspring inherit the grandparents genes, no matter what. Polyandry.
Polygamy seems to be different, for obvious reasons. But even that, is not particularly stable, since it results in an excess of single young men, in a winner takes it all scenario.
Tl;Dr
It is not surprising, in the least, that these folks are an odd lot, and that they have all this drama and heartbreak. Despite the invention of condoms, their behavior goes against our basic instincts and drives.