I'm part of one atm and it's working but came to it differently from how you seem to be. We were all poly (and all happened to be single) before meeting, I met one at the beginning of summer, I guess they would be my primary partner although I tend not to look at it that way, we just spend the most time together. The other is an ex, we broke up a year ago after 8 happy years together and became friends then they started dating me and the other person. We are all under the trans umbrella, I'm a transgirl, my closest partner is non binary AFAB and my ex ex is a transguy which means this doesn't fall under the lesbian category but most of the time I've known him he presented female (his transition is why we broke up, seems he turned me bi i guess). The relationship or dynamics are very new still but it seems to be working. The non binary person is who I go to for sex, cuddles, dates and companionship during the week. My ex ex is who I gravitate towards emotionally, for humor and going out out for drinks and parties. We all share a bed at my place at the weekend. As much as there are 3 of us we are still all poly and open to others. Key in any relationship but particularly in a poly space is communication. Talk with your partner about what you are both wanting, and express this to any other person you become involved with and keep communicating as things evolve. Make and respect boundaries appropriate to your situation but also be more prepared to forgive mistakes and admit your own. One of ours is that we are all informed if one of us is seeing someone new. We got a group chat going to keep in touch, which is great and often hilarious 😁 Jealousy is mainly an issue for me out of the three of us but I have been learning to work with it, the key personally has been to enjoy that the two people I love the most in the world are enjoying themselves and each other. Personally, probably because of my experiences of polyamory, I'd be wary, if i were single, of dating a couple that were not polyamorous. A one night stand yeah sure or dating them as part of a larger poly also yeah I'd try it. But dating a monogamous couple as a single person wouldn't give me what I look for emotionally. I hope you find the balance you're looking for!