The question whether several sex partners should be accepted or not has always been debated, but it is only because we never consider the circumstances.
First of all, the simplest instance is when a person is single. Those who always get sex whenever they want, probably prefer this lifestyle, but those who need stability would probably need a relationship.
And now comes the difficult question: when a person is in a relationship, are lovers acceptable? And is it okay to have several relationships at the same time? If both of you trust and love each other, but you need something extra, then honesty is the key to polygamy. In this case, you might even have a chance for a threesome. What is absolutely unacceptable is to have lovers and lying about them because that is the exact definition of cheating. If you live in a polygamous relationship, than your partner deserves it, as well.
And it might be true that men are meant to aim the quantity, while women aim the quality of children, so to say, but it is not an excuse for those who expect their partner to be monogamous while he has several lovers. And it works the same way around: women should have no excuses if they have lovers and they expect their partner to be monogamous for them.
Polygamy is stressful either if you are committed to your partner or if you are not, but if you still feel the deep need for variety, then at least be honest about it, and if you cannot respect your partner sexually, then respect him or her with the truth.