My wife doesn’t want us to go past kissing with our girlfriend at least for the time being, but the gf wants to have sex she feels like it’s been missing from her life and honestly I don’t blame her. Personally I would rather bring her in with me and my wife. Instead though she asked if she could seek other partners and at first me and my wife were fine with it, but now I feel a strong jealousy starting to form and I don’t know what to do
To clarify: you and your wife are dating a third person, but neither of you will have sex with her. At the same time, you’re expecting the arrangement to be exclusive - she doesn’t have sex with anyone else, either.
This is deeply imbalanced. Neither you nor your wife have made the same promise to her, I’m assuming - you two are still free to have sex with each other, without her. This is not a sustainable arrangement.
Think about where your jealousy is coming from. Jealousy is often referred to as a “secondary emotion” meaning it always has some fear, threat, or other feeling driving it. It’s too vague to just say you have “jealousy” - you need to interrogate that feeling, sit with it, and figure out what’s going on.
If you have a concrete concern: that she will expose you and your wife to STDs; that the partners she is seeking have a history of violence or drama or consent violations; that she has a pattern of abandoning time with you for her new partners - talk about that.
Are you worried that she’ll find something easier or more fun and stop dating you and your wife? In this case, the solution is not to try and keep her through ‘force’ by using rules and restrictions - the solution is to work on the relationship with your girlfriend so what you’re offering is worth staying around for.
Are you feeling threatened by the idea of another person having sex with someone you see as your partner? This knee-jerk possessiveness is common for people, especially men, raised with traditional concepts of sex and relationships. This is something you need to let go of. When we were kids, my little brother hated to share his books. If I picked up one of “his” books to read it, he’d whine, “she’s using it up! She’s using it up!” This is absurd, clearly - reading a book does not “use it up.” He just didn’t like seeing someone else touching or reading his books. Feeling jealous over the fact that someone else is sleeping with your partner in a non-monogamous arrangement is similarly absurd - there is no inherent threat to you or your ability to enjoy time with this partner.
Realize that you, in fact, are in an incredibly secure position. You have a wife. Your girlfriend doesn’t seem to be threatening your marriage. You have way less to lose here than your girlfriend. Realize also that your ability to have sex with your wife doesn’t seem to be threatening your relationship with your girlfriend. Try to apply that same logic to her. If you can have sex with people-who-are-not-your-girlfriend, why can’t your girlfriend have sex with people-who-are-not-you?
Also, sometimes, being a grownup means you have unpleasant feelings that you have to put up with. Feeling “jealousy” does not mean you have an unalienable right to make demands of your partner, nor that they have a sacred obligation to soothe your jealousy. Sometimes we want things that we can’t have. Sometimes I feel annoyed or bored during work meetings, but that doesn’t mean I get to just up and leave. You may be feeling uncomfortable about this, but the solution might just be to “suck it up.” Make the sacrifice of enduring a bad-feeling so your partner can have the same freedom-to-sleep-with-partners-who-are-not-you that you have (remember, your girlfriend isn’t demanding that you not have sex with your wife, and I suspect that if she did, you would not acquiesce or see it as justified).
Please check out this website and all the linked resources for help managing and improving this situation.