Well let me adress jealosy first. It is a fear based emotion but think of it more as a survival instinct. Our instincts tend to be more complex when you've had a child to raise but also become more clear as they on the surface of our consiousness as opposed to a feeling in which can't understand it's origin. I don't for instance feel that any polyamorous relationship should have lovers that are unknown to all involved. As a matter of fact I have witnessed most relationships end this way because we are not comfortable with the unknown factor that is sharing with our partner.
This is a primary difference between swinging and poly relationships. When SO's are in volved in a swining relationship they don't often know their partners lovers. In a poly relationship all of those involved in the relationship also have intimate relationships on some level with their partners. When a new lover is found all take the time to get to know each other to simply be comfortable with each other working towards friendship at the very least.
Jealosy is fear of the unknown. Fear of the possibility of losing someone and fear of inadequacy. But it is entirely natural. Overcoming jealosy is a matter of love, trust and communication. I don't feel it's a matter of letting go as much as being informed and comfortable with a person or situation. The minute we stop respecting our SO's feelings in the matter is the moment that we begin to lose the relationship.
Example: My lover has met someone that she is interested in having a relationship with. I say great, when do I get to meet him/her so I can begin to not feel threatened. So we meet. I like him/her ok but would like more time to get to know him/her. My SO moves ahead disregarding my concerns or needs and jumps in the sack with him/her anyways. This makes me defensive and angry because my feelings were ignored. This will very likely be the beginning of the end because my SO was being selfish and putting their needs/desires before my own when in fact there should have been more respect for how I felt. Worse, it then puts my SO on the defensive and my SO chooses the easy way out with his/her new lover so they don't have to be responsible for the relationship and can start a new one without all the hassle of simple communication and respect.
"Letting go" to me is like building a sand castle only to watch the waves take it away being left to grasp at what little satisfaction is left over from the effort and hopefully a thing or two is learned.
Swinging and Polyamory walk a thin line betwixt the two but I feel the main difference is that all involved have a connection on some level and a commitment on some level. Swinging does not. It's just f*#king the next piece of strange that comes along and tweeks your nay nay. ;}
Now you'll have to excuse me while I go read the original post to see how far off track I got. lol!

So Darkwingedfae, is jealousy just a shorthand for fear in all its disguises then? I've been wondering that myself, as it seems everyone's experience of jealousy seems tied to whatever it is they fear most in their lives.

For example, I no longer fear being replaced. I pretty much get it that I'm irreplaceably unique and so is everyone else. Some other person, no matter what their great qualities, can't really take my place. I'm the only one that can occupy that space. On the other hand, I do have a fear of being left out, excluded, or generally ignored. I can feel more jealousy around that than whether my lover has a special connection to someone else. If I am included in his joy in the other relationship, then I don't feel jealousy and can easily get to compersion. If he keeps the other relationship secret or sufficiently private, I can get triggered, begin worrying, and generally fall into a funk if I don't stop myself and check in with my partner.

"I feel that for me, when I communicate with my SO's about their new loves well and am able to meet the others when possible, the compersion settles in."

Seems to me that the more willing my SO is to communicate specifically about his new and old loves, the closer I feel to him, the less I fear being excluded (replaced, abandoned, whatever the flavor of your favorite fear might be). It is when I'm closest to my love's heart as he experiences joy in something or someone else, that I love him the most. For me, no-one is more attractive/appealing/amazing than someone experiencing and expressing love, whether that love is for me or for some passion in his life or some person he has found who inspires love in him. I feel an expanded sense of myself as a loving being when I feel that love arising in him and am able to rejoice in it. I can't think of a better high myself.

On the down side, no-one's SO can communicate everything there is about another relationship. At some point, I need to wrestle with my own fears. Perhaps when I understand what it is I fear about being excluded, that fear will no longer have any power over me. It's certainly not true that everyone on the planet will seek to exclude me at the very same moment of the very same day. In which case, it's not true that my very survival is threatened. I do have other options. Part of me thinks all these fears have to do with a belief that this is a Universe of Scarcity instead of an Abundant Universe. Is there really a shortage of love? Will I lose it all if I lose this one opportunity to secure enough?

Meeting my love's other loves can help if I approach it from the intent of recognizing how uniquely amazing they are as well. It's especially wonderful if we can share an appreciation for someone new. Unless the other person is giving off competitive or possessive vibes, that is usually enough for me to cease seeing her as any sort of threat to my relationship with my partner. I think I actually begin to imagine we can be enhancements to each other's lives, whether directly or indirectly.

I don't know how this works for people who have a partner who is still dating or creating relationships with monogamous people. Perhaps those vibes are always going to be there for them. I no longer get involved with people who are not committed to openness in their relationships. Our socialization in this scarcity model of relationships and the social supports for it can carry such weight that it often takes a conscious effort to overcome these fearful responses.

Perhaps those who rarely experience jealousy can tell us something about how they have avoided the socialization which says that jealousy is proof of a greater love rather than sign of some unexamined fears?

Well said Barbara!