Interesting thread.
Personally, I think that it depends on what the relationship is driven by. Is it a mere physical attraction - lust? Or, is it by a desire to be with that person because of who they are, warts and all - love?
In Western society, and as a large result of the media, i.e. TV and Film, a worrying amount of people mistake physical attraction for love. Of course, physical attraction is part of a relationship, but love itself needs to be nurtured and cultivated. Not only that, but it needs to be reciprocated. How else can a relationship grow if feelings are not reciprocated? Then, once the initial 'magic' has worn off, the relationship sadly crumbles. Relationships, like everything else, need work.
As for polygamy itself, I think it would be very difficult to manage. A person, male or female, would have to have a great deal of integrity, and would have to be a very loving, honest and compassionate individual. Having said that, it works in various cultural settings. For example, the Masai tribe in Africa are Polyandrous, a form of Polygamy where a woman has more than one husband. In this setting, the Wife has one husband that stays at home to look after her, and another who spends the majority of his time in the wilderness hunting and gathering food. It has clearly worked for them, and for a very long time.
