Hi, I figured I'd post here for some advice since none of my friends are really involved in poly/nonmonogamous relationships.

TLDR since my post got super long: I've never been jealous in a relationship before but now I'm feeling jealous and insecure about my partner's budding romantic relationship with their friend and I'm not sure what to do. I've been trying to ride it out but me ignoring my feelings is worrying my partner and causing them stress. I'd really appreciate advice on how to work through my jealousy and insecurity in a healthy way (and maybe even some advice on healthily communicating with my partner about these things)

I've been with my current partner (T) for a couple of months and I'm now experiencing jealousy regarding T's relationship with their friend (D). I've never felt jealousy in a relationship, so I don't know what to do in this situation since I don't want to be jealous and insecure regarding their relationship and I don't want it to cause problems for me and T's relationship bc that's not fair for T or D. Plus I really like D and they're a genuinely great guy and we've slowly been becoming friends as well so it's not like I have any issue with them. For context, I've dabbled in nonmonogamy for about three years including: throuples, open relationships, bringing in thirds, and being the third. I'm not entirely sure why I am now feeling jealous in this relationship when I haven't in previous relationships.

Initially, I wasn't jealous of their relationship, I was completely fine with them going on dates and kissing/cuddling. T likes going on dates and occasionally kissing friends and I've never had an issue with that. The jealousy started when out of the blue one night T asked me if they could go further than kissing and I felt uncomfortable and jealous about the idea, they of course respected that and now we've been trying to figure out why I felt that way and how to work through it. But since I'm not used to jealousy I haven't done a great job of knowing why I feel the way I do and what to do about it, which has led to T being worried about hurting me and making me feel insecure. And I hate that they feel that way bc they haven't done anything wrong. I think my jealousy and insecurity may come from the emotional aspect of the relationship and that's why I was uncomfortable with them having sex, T only has sex with people who they have an emotional/romantic relationship with. We were talking about it again today (they ask me about how I'm feeling with the situation every time they plan to hang out with D), and they told me that they definitely did like D and described their relationship as kind of a situationship. They told me that what they like about poly is the different types of relationships they get to have. And when I brought up that I don't know if I'm comfortable with them having romantic relationships with others they said that was unfair since they need that emotional/romantic to get with people and I completely agree with that and I absolutely want to be comfortable with them having other relationships.

On the other hand, I haven't been with anyone since we got together. I don't like going on dates with someone I'm not actively in a relationship with since I don't like the expectations or pressure of going on dates since I'm very slow to develop feelings for people (and frankly I don't think I have the emotional bandwidth to be in a relationship with more than one person). I prefer NSA hookups, but I haven't done those since we started dating since I don't want to bother with finding a possibly mid/bad hookup when me and T already have a good sex life. I also definitely won't start anything that's not strictly platonic with any friends since I have a general rule that I don't make out/hookup with friends, plus a majority of my friends are lesbians so that's an obvious no. The most I've done while we've been together is make out with one of T's friends at a bar. So basically, things feel kind of uneven since most likely I won't be doing anything with anyone else which may also be part of my discomfort since T is going on dates and building a relationship and I'm not. I've been debating if I should try going on some dates to make things feel less uneven and I feel less like the weird guy that stays at home while their partner is out on dates and doing stuff with people. I don't like going on random dates but I haven't done it in a while since I dislike them so I'm wondering if I should give that a shot and see if I feel differently.

So sorry for the long ramble but I felt like I should give context for better advice. But basically my newfound jealousy and insecurity hasn't exactly been great for our relationship and is causing T a lot of stress bc they're worried that they might hurt me. We're trying to figure out ways to help my jealousy and insecurity other than me ignoring it and trying to ride it out until I stop being jealous bc they think that'll come back to bite us in the butt and they're probably right. If anyone has any advice or anything to help me work through my jealousy in a healthy way so it doesn't continue to be a point of contention in our relationship it'd be greatly appreciated.

Thank you in advance :)