partner wants to do smth i don't, and i feel bad saying no
I'm gonna be fully honest here, so here we go.
I'm (M20) in a relationship of over a year and a month now with a girl (F19) and she recently started asking about a threesome. I've done one in the past and didn't really enjoy it. She asked a few days ago and I didn't like the thought of sharing her tbh. I'm quite a jealous guy in that respect.
Anyway, she kept asking because i kept saying "i'll think about it" and a few days ago she asked and when i said "i don't think i want that in our relationship" she seemed a little bit disappointed. not that that's unjust! of course there's going to be a bit of disappointment every now and then, but it just made me feel a bit shitty.
so, i broke down a bit and said that i was worried i wasn't doing it for her anymore. she told me that she wouldn't have moved in w me (we had a 2 week break recently due to my f*ck-ups) if i didn't do it for her anymore and she entrusted me with getting my shit together and blah blah blah. Anyway, today, she asked again and I thought she was js being teasy and cheeky, so i said "you do more than enough for me" yada yada yada. then, she seemed sad when i said no. so, i asked her to list every fantasy she has rn and we'll see how i feel about them. there were 4, 2 of which i liked the sound of. the other two were cuckolding (we're both switches) and a threesome.
I asked her why she wanted to experience a threesome so much and why she'd been asking and her reasoning was "I want to experience it whilst I'm young". Fair enough. I told her I'd think on it.
Anyway, fast forward to a couple hours later and she's now running ideas as to how to make it a bit easier for me to enjoy it. She suggested, and I quote: "I try with a guy who's down to include you and knows about us/you, WITHOUT you first to see the vibe."
I just feel like I'm not doing enough, sexually, for her and I worry that she is just looking for an excuse to do it with other guys. Because, during our break (we technically split up) she slept w a couple dudes. Now I'm just worried I don't really get a say without feeling guilty. Especially as she said it was "a bit poopy :(" that i said no.
I know she probably means no harm and is just excited at the prospect, and good on her for being open to sharing her fantasies, but I just worry.