Well, being one of the few monogamous people in this house, I have a slightly different take on jealousy. I like to distinguish between a desire for romantic exclusivity and possessiveness. Both are often referred to as jealousy, but they are not the same thing.
There are somethings that only my girlfriend, Irene, and I share with each other. We enjoy having aspects of our lives that are kept special and private. But that does not mean that we own each other. Irene is an adult and she can make her own decisions. If I start trying to control her in order to preserve that "specialness," I am not treating her with respect, and that does more to hurt our dynamic than her spending time with other people.
Of course there are times when I feel like I don't get to spend enough time with her. But a simple conversation can quickly fix that. Treating your partner with respect and good communication can go a long way to solve jealousy problems.