I have never been a "jealous" person when it comes to relationships. When I hear people use the term it usually refers to someone feeling bent out of shape when someone they are connected to emotionally (usually romantically but sometimes platonically) is seen to be receiving the attention of someone else. The connection can be current, or a remnant of a previous, but still smouldering, relationship.
One has to remind oneself that jealousy is an emotion. And like all emotions, it is not rational. In other words, it is not an intellectual realization that can be thought away so easily. When someone feels jealousy, they are being informed by a very primitive and basic part of their brain that undoubtedly served an important purpose in our evolution.
It's important to recognize possessiveness when talking about jealousy in the context of relationships. Jealousy and possession are co-pilots. When you see, for example, your current or ex-girlfriend having a nice (even flirty) conversation with someone else (maybe a potential suitor in your mind), your amygdala goes on alert and you prepare to fight. But what are you fighting for? In the most basic sense, you are fighting for someone who you must feel you have some ownership over. Right? Whether or not you actually believe this in the moment, that is what is happening. As we evolved and took mates, it was beneficial to ward or fight off other individuals who could be competition for your sperm or egg. It made evolutionary sense. But humans have the capacity to move on from this base instinct, and we need to dig deeper into where it comes from to get through the fog of jealous emotions.
When one steps back and considers a feeling of jealousy, and connects it with the instinct of possessing a mate, it becomes very clear that this is a false belief. No one can possess another person, at least not legally in all civilized societies. Of course, in the world of D/s, "owning" a slave or submissive is a very common reality, but is part of the fantasy of the power exchange. A girlfriend, or wife, or close friend, is not something you can ever own. They are their own person, a free agent, who can do whatever they want.
So if we continue on with the characterization of a jealous response as a threat to one's perceived ownership over another, we have to think about why the threat is perceived. Why is it a threat? Anyone you perceive as a threat is obviously someone who possesses the same or better qualities as you, right? Otherwise why would you be worried? A jealous person is reacting emotionally to the idea that the competition will take their possession away. And if we go even further, I would argue that the feeling of a threat is based on a feeling of inadequacy, which goes straight to a lack of self esteem.
Think about it. If you believed that you were not inadequate, you would not perceive the other suitor as a threat at all. What possible concern could you have if you knew that your qualities were not something anyone else could possess in the way you possess them?
So now that we see that jealousy has nothing to do with anyone else but ourselves, we need to examine our self esteem, think hard about what makes us worthy and unique, and start to build ourselves up in our minds and realize that we are all amazing in our own way and that no one could possibly compete with us.
Careful, though, don't let this go to your head. You can be self-confident and humble at the same time. Self-confidence minus humility equals arrogance. And no one likes that.
We've only been talking about jealousy and monogamous relationships to this point, but what happens when we add multiple intimate partners to the mix? Sounds like pouring gasoline on a fire, doesn't it? Unless you have your jealous instincts sorted out, it's a recipe for disaster. And even the most experienced, self-aware, psychologically sound people in poly relationships sometimes get jealous. But they know that this instinct is just that, an irrational emotion based on primitive parts of our brain getting activated. The solution is to identify the emotion, let it in, think about where it comes from and then allow yourself to realize that there is no reason for it. A calm, adult conversation about it usually follows, with perhaps some boundaries set. But there is at least the acknowledgement of something that is not quite right.
I am in a relationship right now (my marriage to my wife of 13 years) where we both have other partners. Her relationship with her other partner is hers and hers alone. It has nothing to do with me. I respect her connection with this man and she respects our marriage and our personal relationship to each other and the family unit. I, too, have had multiple partners, mostly kinky play, and she respects these arrangements for what they are. No one could ever come close to her in my mind in terms of a life partner.
I have also been a submissive in a D/s relationship where there were other slaves in the Domme's domain (harem?). I knew my place and knew that none of the other submissives could ever possibly "replace" me. How could they? I am unique. But so are they. It goes both ways. The attention I received from my mistress was the attention she felt she needed to give me. And if I didn't feel like the amount or quality of attention I received was adequate for my needs, I had the ability to express my feelings and leave the relationship if there was no middle ground
Before concluding, I think it's important to make the distinction between envy and jealousy, as they are different things in my mind. Jealousy is an irrational emotion, whereas envy is more of an intellectual realization of someone else's situation that you would very much like to be in. I experience envy all the time, and am usually successful in focusing instead on the blessings in my life, but also with the knowledge that how you perceive someone else's situation is rarely their reality. That billionaire on the mega yacht might not have a single loving, nurturing relationship in his life and could be on the verge of a mental breakdown from the insane lifestyle he is leading. Who knows?
So if you find yourself feeling jealous, turn your attention away from the people involved and look inward. Ask yourself why you feel this way and what you could do to increase your self esteem. Maybe it's stopping something that makes you hate yourself? Start there and be gentle with your mind and heart. Once you realize that you are enough, and do not need to compete, you will become so much happier and will have the capacity to love more openly, freely and unconditionally.
You can do it.