Jealousy is a monster and I don't have it. My ex did but she was not rational about it. My examples are that a couple knows where the other one is most of the time. Each of you know who you are coming home to. A person gone an hour or more doesn't mean anything. My wife and I could spend half a day in a store. For the most part, people do not do the rush and quick fuck that you see in the movies. What would they be getting out of that? Half the time it doesn't even have anything to do with the movie and less to do with real life.
I once had a girlfriend that was upset that I'm not jealous. Her and a friend of mine got together just to change that and make me jealous. They planned out a sceme on the phone. I found out and told them both to stop. My words were "this is a game that I do not play." In that case the girlfriend actually wanted me to be jealous. Insecurity proves nothing.

Some years back I interfered in the relationship of two people in what I believe was an inappropriate manner. I think I caused pain to others because of my pernicious jealousy.
Today, looking at these two people, and realizing what is currency in the world of dating, the man, who is older, looks fit and appealing. The woman, who I realize to be both talented and brilliant, looks terrible. She has bad rosacea, an unflattering haircut and in gaining a lot of wait about age fifty, looks awful and bloated. The weight gain does not suit her. The once cute couple does not speak anymore and he's moved on to younger and cuter women. Also smart and talented. He's a grandpa; his ex is childless.
I still feel guilty and am not now friends with either and won't be meddling further in their lives. I cannot allow myself to be jealous. What it did to me is ugly and I was ugly myself.

I have to battle the green eyes monster. I know it is my own inserurity, combined with the fact that I have been cheated on a few times. Strangely though, a couple of times partners have expressed extreme jealousy, and I found out later they were cheating at the time.

None.

I have never been jealous, nor have I understood the emotion. I like the people around me to be happy and enjoy their lives to the full - why should I be upset if they are happy and having fun?

My ex was actually jealous of my farm! She tried to decide, for me, what my crops needed and didn't need. How crazy is that? Good riddence to her.

Sometimes it's insecurity, but sometimes it's justified and caused by your partner's actions and/or words. Sometimes it's even projection. You can tell when your partner is in to someone else though. We feel what we feel. I don't think you can actively change that. EDIT: I guess it's always insecurity when you think about it.

I have never been a jealous or suspicious person. I have always had more male friends than female and the same with a couple of exes. I found out after a 10 year live in relationship that was on and off that he was cheating with a girl in her twenties and had tried to pick up two friends of mine. I ended that 9 years ago and am happier and freer now.

I don't get jealous, but my ex was over the top jealous and it contributed to my leaving. I blame myself. I saw it raise it's ugly head once before we married and I should have left then. When someone gets over the top goofy once it will most likely show up again, and again, and again....

Very rational if your not paranoid but how would you know and a cheater would always try to make you think you are. My tip, if your in doubt, get the fuck out.

I believe jealousy is a side effect of insecurity.

That said, I believe a partner's actions can influence the other's sense of security in the relationship.

When I am in relationship, no matter the situation and no matter how friendly and warm and welcoming I may be, I intentionally never do anything to disrespect my partner or our relationship - or to in any way signal that I am -- or might be -- available in any way whatsoever.

To me, if both people are doing that, jealousy should be a non-issue.

I didn't used to have this insecurity until I got married and my husband cheated on me both emotionally and physically with numerous people. He also became abusive and said terrible things that eventually made me think I was crazy, not trying hard enough, no one else would want me, etc. I almost lost my life at the hands of the man I deeply loved, so after I left him and dipped my toe back in the dating pool I found myself having panic attacks when guys would spend too much time on their phones or behave secretively. I know that I can grow out of it with a partner who proves to be loving and trustworthy like my first love should have been, but I also know that insecurity will be a big hurdle to get over as I move forward with dating. I think jealousy and insecurity are a highly personal issue always born from witnessing infidelity or wanting to be unfaithful. I know men who have accused partners of being unfaithful because they are secretly insecure about their own unfaithful desires and behaviors.