Siamese twins share.

Conventional wisdom says that jealousy is a negative feeling that stems from insecurity. I say that’s a huge generalization, and that jealousy, like all feelings, is both valid and necessary.

The feeling of jealousy is very complex. For me, it’s always about someone else encroaching on something that’s mine. That implies possession. It implies that when I’m in a relationship, I have some ownership over my significant other. Being in a relationship means I’ve added another set of legs and arms and brains to my appendages. And no one shares their appendages. This is when it becomes rough to see one of your appendages do something you thought you weren’t going to do. When you’ve assimilated someone so deeply into you that you think of them as yours, it’s hard to see that they may want things that you did not think they wanted originally. This is where jealousy comes from in my book, and it’ s why jealousy makes sense as a warning mechanism of a relationship not working the way you want it to. Jealousy in this sense is a tool to improve things, and a very valid resource to use to make a relationship whole.

Selfishness may be the deepest and oldest root of the jealousy tree despite getting such a bad rep. Among polyamorous circles, selfishness is a negative thing without a doubt. I’ve no experience, but I imagine that if someone in a polyamorous relationship is jealous, the relationship can’t be maintained. The people in a polyamorous relationship have agreed on sharing very specifically. If it’s someone monogamous, then jealousy is entirely natural. No one has agreed to share, and it’s very unlikely those boundaries have been determined or even talked about. A pang of the jelly belly might just be a warning that those boundaries have to be talked about soon.
Jealousy is just not at all about insecurity or a negative feeling to be eliminated. Feelings make sense whether you know they do or you don’t, and it’s up to every individual to figure them out in order to have a good, healthy relationship.