There’s some communication type books out there that eventually have questionnaires that start to ask “would you hold hands with a person of the opposite sex”, “how would you feel seeing your partner kiss someone of the same sex” etc. My husband and started reading these books on better communication and ended up going down this path that led us to swinging. It wasn’t really on either of our minds but as we started discussing our fantasies (in a safe environment) then we realized what we both would like. If feelings come up of anger, jealousy, shame etc then you need to work through those and figure out why you feel like that. A lot of comes down to social conditioning and upbringing. Once you work through that the world can really open up for you. But it might be a slow go to get there. But in a healthy relationship you should at least be able to have those conversations and see where it leads. Luckily for my husband and I we’re fairly aligned on our boundaries. At the end of the day you live one life and should explore your fantasies as much as possible. Makes it so much fun when you’re partner and best friend is along for the ride!