If you think polygamous people are less possesive and jealous i have quite some stories to tell about the polygamous people i know. Polygamy in theory requires an emotional matureness that i have yet to wittness in practice. All the polygamous people i know either had more of a harem idea, with them having many devout sex partners or were just unable to form strong and commited relationships.This goes for all interpersonalrelationships, not just sexual ones.
I cannot judge if there is people able to live it like envisoned, but the ones i know are basically children that didnt learn yet, that you cannot have every toy in the store.