How would you handle this?

A couple of years ago, my wife got the idea that maybe we should open our marriage. (We married young at 18 and 20. Never went through a "wild oats" phase. We've been married nearly 20 years now, currently in our mid- to late-30s). After about a year of gentle pushing, she convinced me to give it a shot last year.

Since then, she's had several relationships with men, usually short-term, casual and centered largely on sex. I'm cool with that. Turns out I'm really good at compersion.

Also since then, I've fallen in love with a beautiful, wonderful married woman. It's a deep, meaningful relationship - not just sex. We're both demisexual and bizarrely similar in many ways. We can relate to each other like no one else we've ever met.

Both my wife and my girlfriend's husband continually go through phases of complete freak-outs over it. They both have insecurities and worries that show up as jealousy. They'll be fine with polyamory one day, then completely despondent the next.

It feels like a see-saw. When my girlfriend and I experience happiness going up, our spouses' happiness goes down. If we placate them by pushing pause on our relationship or setting sexual/physical boundaries, we feel manipulated and unhappy ourselves. I resent my wife for having multiple relationships with men but not allowing me the same freedom. There doesn't seem to be a good solution.

My girlfriend and I are also both very happy with our spouses. We want them to feel secure and happy, too, but that's been elusive so far.

I don't know how to handle this situation. Thoughts and suggestions would be appreciated. They don't teach this in adulting class :)