Threesomes?

How do those in a relationship feel about threesomes? I’ve had several in the past but I have always been the girl who joins the couple. I’ve never been in a relationship while participating. I’ve always just joined my friends or friend couples.

But now I’m in a serious relationship and we’ve talked quite a bit about finding someone to join us. I’m just nervous about how it will effect us. I’m very confident in my relationship with my partner and our relationship is strong. We’re very open and can talk about anything so I’ve voiced concern worry but I always get reassured that nothing would change it will just be a fun experience. I am excited thinking about it but then I also have this sick feeling in my stomach.

I’m worried that after I might regret it or get jealous or something and there’s nothing I can do after it’s done. I don’t know, anyone else relate?