I (27F) don't know how to deal with my bf (20M) wanting to open our relationship after 2years

So, my boyfriend and I are together for 2years now, minus a few days. We share a flat since last September and everything is going very well. We met at work (in a campsite) when I was 25 and he was 18, started as friends then it escalated quickly and we became official. Spent less than a year long distance, I'd stay with him for a few weeks and he would came for shorter times (he was studying I was freshly unemployed). From march till September 2024 we started working together at the campsite again, thus living there together, sharing the same group of friends/colleagues and doing pretty much everything together.

I always loved my independence, I lived alone for some times when I was younger and I likes it a lot, needed some time alone often, him not so much, but I was ok with that. Then September 2024 he got back to studies, and we decided to share a flat, for reel this time, I crossed the country, left friends and family (even though I'm long distance with most of my friends abroad anyway) and moved in with him. During all the school year, he'd go to class and I'd work remotely all week long and because we changed city and didn't really know anyone else there, we stayed a lot together, spending our free time together.

I started a new job at a campsite again in march 2025 and he joined me there beginning of July, once again living together and sharing our colleagues made friends. We tried for the whole month of July to spend as much time together as possible as our shift were complete opposite compared to before years (him at the restaurant and I working more office hours). It was good, great even, as per usual. He started going out more but I couldn't blame him, I'd be asleep most of the time when he'd come back from work and he'd be sleeping when I was off to work in the mornings so fair enough.

A few days ago, he asked me how I'd feel opening our relationship. I was more than surprised. We'd talked together of, later in our life, trying other stuff but more in a together way, never in a you do you I do me kind of way. I said I needed to think about it. I know he's bisexual, me.too, and he never had experience with boys neither do I with girls so I knew he'd want to try it someday.

The thing is, I know he's young and we met when he just turned 18, so I don't want him to feel like he's wasting his youth with me, and we had this talk, so after thinking and putting as rule no-one I know and will possibly have conversation with, I said yes. I said yes to make him happy, I said yes cause I thought I could handle it and I said yes because it was a fair trade. He can go to other but I can too of course, even if I already know I won't do it, for now at least, I have a lot of things in my mind and I'm not at my best at the moment so I definitely don't want to go and meet people.

But it's been literally 48h since I agreed and I already have a massive anxiety bubble in my stomach, I cried hard yesterday and today, probably tomorrow too and I can't focus on work as well as I could. I'm thinking about it all the time. I'm trying to think of new rules that could help me but for the very first time of my life I'm jealous, never happened before. But now I want to check his phone, look at his tinder matches, see the people he talks to and I don't know if I can handle it for long.

I'm looking for advice on people who have been in this situation, how did you cope, does the jealousy ever goes away ? If it happened to you, did you decide to shar with the other person what is happening on your and their side or did you decide to not talk about it and let the person have their thing without knowing ? I'm really lostand I am looking for advices.

Also to mention, I'm having a hard time with my best friends at the moment and the people I see every day are also the ones my bf sees every day and I don't want to rant or ask any of them cause we said we wanted to keep a low profile so people I can see having something to say with the way we handle our relationship don't put their big noses in our business.