Written by Emily Nagoski, Ph.D.
Okay, so jealousy is made of two things: lack of trust for your partner AND/OR insecurity about yourself. Let's take that in parts:
There are essentially two reasons why you might not trust your partner.
First, your partner might be genuinely untrustworthy. In which case, why are you in that relationship?
Second, you might just be slow to trust. Maybe you got burned in a prior relationship, maybe you have an insecure attachment style, or maybe you're just naturally cautious. All of us have our own pace for building trust and you can only allow trust to grow at the rate that's right for you.
One way to build trust is to have occasions when your partner could potentially violate your trust but doesn't. Small things like being where they say they're going to be when they say they're going to be there or remembering to do something they said they'd do, these are safe opportunities to allow trust to grow.
Jealousy due to insecurity about yourself works this way: your partner goes to work or online or to hang out with friends and your brain starts to spin with thoughts about how they'll find someone better than you, someone prettier, skinnier, smarter, saner, sexier, longer legs, longer hair, bigger boobs, who doesn't have any emotional baggage, etc.
If this sounds familiar, know this: doubting your worth will make your partner doubt your worth. Knowing your worth will make them know your worth.
The cliche about not being able to love anyone until you love yourself is painfully true. Those who can't love themselves are the most in need of love, but their own self-doubt acts as a wedge between themselves and the connection they crave.
First of all, what NOT to do is to make rules about what your partner can and can't do so that you can feel okay. It's YOUR jealousy, therefore you're the one who has to take responsibility.
"But they're in a relationship with me! They HAVE to help me!" No. No, no, no and no. They are likely to want to help you (and I would worry about a relationship where a partner is not interested in helping the other to feel more functional in the relationship), but no one is ever under any obligation to help you until they agree explicitly EACH TIME. Being an adult is being responsible for meeting your own needs.
So. You ask for your partner's help to create an environment where you can let go of your mistrust and/or insecurity.
"Partner, when you go out and spend time with your friends without me, I feel jealous and insecure. It would help me if we could find some sort of compromise, like if you go out, you could maybe call me at 10:00 and check in?"
"Partner, when you talk about that co-worker, I get jealous and worried. How about if I could meet this person and then the two of us could go out together for the evening?"
Such compromises and collaborations should function as scaffolding while you train yourself to stay over your own emotional center of gravity.
I must add, however, that it won't be easy. At times, it's going to suck. You are going to have to take a lot of deep breaths. You're going to have to call friends to talk you down from calling or emailing or visiting inappropriately.