In my opinion jealousy is fear; fear of losing something one has or fear of not getting what one feels entitled to. We teach our children not to be jealous of each other and we extol the virtues of not being jealous in our society but for some weird reason we, as a society, cherish jealousy in romantic relationships. If your child is jealous of your newborn, society would condemn you for getting rid of the infant to show your love for your older child but if you refuse or throw away a lover (or potential lover) to prove your love to another lover, the same society applauds you.
I think the jealousy culture regarding romantic relationships stems directly from a patriarchal society.
As to how I deal with jealousy in my non-monogamous relationships - I try to unearth the cause of the jealousy and deal with it rather than removing the stimulus that triggers it. If my partner is jealous because he is feeling insecure, I provide reassurances that he is still valuable and loved. I may be wired oddly because unless my partner refuses to do something with me but then seeks out a different person to do that very thing with I don't feel jealous. That hasn't come up with my current primary.
If all partners are open about their feelings, jealousy is probably something that can be overcome.
we, as a society, cherish jealousy in romantic relationships.
Sad, isn't it? I've had male ex-friends tell me we could no longer be friends because "she just wouldn't understand". I can't imagine getting involved with someone who would be jealous of my old friends or ex-lovers.
I've always liked the bit on the Alt.Poly FAQ about jealousy:
Subject: 5). What about jealousy? Some people seem to have no jealousy; it's as if they didn't get that piece installed at the factory. Others, including some long-term polyamorists, feel jealousy, which they regard as a signal that something needs investigation and care, much as they would regard depression or pain. Jealousy is neither a proof of love (and this is where polyamory differs from possessive or insecure monogamy) nor a moral failing (and this is where polyamory differs from emotionally manipulating one's partner(s) into relationships for which they are not ready).
It seems to me that everyone likes to feel special, unique and important, and that we as people cluster together our anxieties about feeling unspecial and try to dump them on one chosen person at a time. When we stand the chance of losing that support system, even for a bit, we're not sure what to do with ourselves. Perhaps jealousy is a mark of our own insecurity magnified by fear of losing the person(s) who allow us to deflect that insecurity most easily.
It almost always backfires, though, as jealousy is the least attractive of emotional states.
Jealousy shouldn't be considered a good thing or necessary in a relationship, but in polyamory there is the danger that since jealousy is considered unhealthy, people will hide their jealousy or be in denial of it. I've had it happen where I rationalized and told myself "no, I'm not jealous", but then I kind of flipped out later and realized oh wait, I was jealous...either that or it was "I'm not jealous...wait a minute, then why do I keep thinking about it and feel kind of weird...oh shit, I am jealous" although with that I kind of admitted it and got on with my life.