First and foremost your partner is polyamorous, just because you want to close the relationship doesn't mean that your partner is going to close the relationship.

Second I don't understand why you think being polyamorous means you're doing things with your meta that sounds like kitchen table polyamory, Even then you really don't have a relationship with your metas.

Metas are the people who are also dating your partner but aren't dating you.

Third off, you're saying you're jealous and insecure, you need to talk to your partner about your jealousy and insecurities.

it sounds like you're trying to protect Your jealousy and insecurities by switching to monogamy.

Let me tell you right now, switching to monogamy isn't going to make it better, it's just showing how toxic you're going to be.

Because your partner is polyamorous, even if they try to switch to a monogamous relationship, that doesn't mean they're not going to have feelings for other people. So if they flirt, or look at another person. You're insecurities are going to rare their ugly head and it's going to be extraordinarily toxic for your partner.

Talk to your partner about your jealousy and insecurities. if You can't, then you don't belong in a relationship of any kind.

You can also talk to a therapist.

PS if you went into the relationship polyamorous, and You decide to tell your partner that both of you should become monogamous and they drop their partners because of your insecurities...

your partner is NOT going to be like hey I'll just drop off all these other people who I'm interested in because you're insecure..

so you can pretty much expect them to drop you so that they can continue to see those people.

that's what I would do, cause I'm polyamorous for a reason.