That's more or less what got my wife started in it, not lacking attraction to one another, but wondering about others. We loved each other to bits (still do in fact!) but we'd only ever had each other in that way. We were curious. Started as swinging, but eventually we settled more into poly with a dedicated side piece for each of us that we have strong feelings for too.
For us at least, it's completely normal to be madly in love with two people at the same time. Maybe even more to be honest, but we're happy with what we have and don't want to rock the boat further. We're still #1 for each other both emotionally and legally, and always thought we'd only ever be that connected to one another. But when it became obvious for both of us that we had "caught feelings" to use the phrasing the kids use, well, we were still madly in love with each other and had less than no desire to split up and all the emotional and financial hell involved with that, so, we have each other, we each have a side piece, and occasionally we even double-date too.
Idk, it's fun. I have two women in my life that bring me joy and my wife has another man that does the same. I'm sure it's not for everyone but I will admit that I find myself wondering how many marriages that end in infidelity could've been saved if the people in them just accepted that it was pretty understandable to not remain completely 100% committed to one person for the rest of your natural life.