Jealousy boils down to fear of loss. I'm usually not capable of this emotion, because I just don't feel possessive of other people. I don't want to own anyone's sexuality either. I do prefer monogamy. I feel very safe and secure within monogamy, and have no trouble committing.
However, I did marry a man who was never sexually compatible with me. A few years in I realized I actually had a psychological and emotional need to have regular sex, and the near celibacy he turned out to be capable of was unhealthy for me. But I was in love with him, and divorce wasn't even a consideration at the time.
In my case, I had unwittingly married a gay man. My reputation for running hot within a relationship made me the perfect cover story. Can't be gay married to a pretty, feminine, shapely woman who loves to fuck. Right? I didn't yet realize he was gay. So we went ahead and opened the relationship.
He was mostly okay, occasionally jealous, but I stuck to the rules. Be discreet in public. Use safer sex practices for intercourse and anal. No partners who seem to have iffy judgement or too distant a relationship with honesty. Only partners who promise to follow those same rules with any other partners. Be home, bathed, and in our bed before he woke up. We each had veto power; if an outside partner made the other spouse uncomfortable, they had to go because our marriage was the only priority.
This worked just fine until I figured out he was gay, and we were never going to have the monogamous marriage I thought I was signing up for unless I wanted to go back to celibacy. He's still in denial that he is gay. He's still probably willing to do what he feels he has to do a few times a year. I'm not interested in that. He is still the best friend I ever had. He still wants to remain married. So, I stay. I have two discreet relationships on the side. Since we no longer share a bed, I no longer worry about being in bed before he wakes. I can tell he needs to snuggle more than I want. Honestly, I never want to snuggle with him. I just dont have any snuggly feelings for him now.
Anything to which a couple might subject their relationship should have goals that outweigh the risks. For us, I had said point blank I needed to have sex sometimes. And by sometimes, I did not mean the three or four times a year he provided. I said he had missed a perhaps critical phase of personal development by never having dated anyone but me as an adult. I had presented my hope that through sex with others we would each learn about ourselves and giving and receiving pleasure, and bring those lessons home to improve our sexual connection. I had also asked if it was fair for me to expect one man to fulfill all of my needs.
I don't believe I would ever have figured out he was gay if we had never opened the marriage up. I think I didn't want to know. Lots of stereotypical signs were there for me to see through the lense of retrospective objectivity. I think I wanted to miss those signs because I loved him so much.
I still love him just as much, but now that love is sisterly. I love him like family, not like my man. I don't guess I'll ever feel that way about anyone again. It doesn't matter if I do. I'm not leaving my husband, so I hope I never feel that intense, romantic sort of love for anyone else again. He has ruined his back providing a good life for us. I will take care of him when he is old and less mobile. He deserves that much from me. His loyalty is not ever in question, and I regret the pain I caused him for years because I said I was going to leave. He never wavered in his dedication to my safety, security, stability and happiness. He loves me very much. I don't think anyone ever loved me more except my mother, aunt, and grandmother. He just lacks the lofe experience to see that he just loves me like family too. It may not be the life I wanted, but recent observations have reminded me how good I have it. I could do much worse than spending my life beside my very best friend.
It is possible that I would have benefitted from never figuring out his secret. I was very pleased with him right up until I did. Over time he was getting better in terms of sexual performance. Perhaps given a few more years he also would have learned to respond to my overtures more often, and make his own more often too. If he's fine pretending at heterosexuality, and if he had gotten better at the ruse, in my ignorance I would have remained happy, and believed we were just growing closer with time, as is natural.
So. What's my point for the OP? You need to really know yourselves and each other. There needs to be clear goals. What exactly is the point of the opening up? What precisely do you hope to gain. What would make you feel threatened, insecure, jealous? Do you have any sense of possessiveness? Have either of you ever cheated on a partner? Can you form a consensus regarding both the goals and rules? How open are you to renegotiating the rules as you learn about yourselves, each other, and the way extramarital partners impacts you and your relationship in unanticipated ways? What, if anything, could you possibly learn about yourself or each other that would change the whole marriage? Consider things you can't even imagine are true, but if they were true, this would all be a waste of time.
Answer these questions together, and put your love first. Maybe opening up is right for you. Maybe it is best left to fantasy.
Best wishes.