I feel like a party pooper

My partner (F36) and I (M35) have been together for three years, engaged for two, and are nonmonogamous. We have dated other people, and it been fine. There's been an established cadence to things, that have made it seem like we have really "done the work" to decondition ourselves of societal norms. We've had disagreements, and been able to talk about them with compassion and a drive toward understanding. She has been the best partner I have ever had. And The security we have created for each other allows for expansive experiences outside of her and my bond. It's felt idyllic.

However, a couple of months ago - by chance, we ran into an old flame of hers, from when she was 16. A guy she had a crush on, and was teased for crushing on, and "cock blocked" when he came to visit her at her boarding high school, when she was 16. The unrequited crush has been a large part of her rationale behind what's felt like a highly accelerated progression of relationship with someone whose existence has only just become something I know of. It's taken alot of conversations to recalibrate amidst the shifting landscape. And as of a couple of days ago, she had the bright idea to assuage some of my concerns by doing the "Relationship Menu" (which we learned of from the Multiamory Podcast), where you list desired components of a forming or established bond with another. The uncertainty and "idk's" of it all felt, finally, acknowledged and addressed - to a degree. I was content in simply processing the changes laid before me.

The next day, however, while at work just chatting with some co-workers, my partner's pending partner came up (in a completely unrelated context - I am not out as poly at work), and his age was made known to me. Which made me think of those younger years of my partner's connection with this person, and reflect on how that age difference was a man pursuing a child (mid-college aged person visiting the dorm room of a 15/16 y.o). It's created this confusion and unsettled feeling in me, where I am wondering what role or impact that dynamic had on her past, and on her present self and feelings. Especially when she has a history of being taken advantage of, by men who she thought were safe.

The constant conversations about this topic have really worn us both out, and I don't want to keep at it, when my desire is to reconnect (and stay connected) to her. I have to admit that the prospect of simply and comfortably accepting this potential dynamic with her and this person is difficult for me to parse. She has said that she has much reflection to do, on the matter. It's just that those words have been used at the end of all of the conversations around this bond, and it's still progressed - so I'm trying to prepare myself for the likelihood that it'll still be the case, even now. I don't want to control her, or dictate who she loves or connects with. I love and support her individual journey. I just have this gut feeling that I'm struggling to push through. I find myself fixating on the morals we've discussed as shared, and how this falls out of alignment with what I thought was how we mutually saw the world.

I know that alot of people bash and criticize, on this platform, but I'm an open-hearted man, simply trying to be the most loving member that I can be, in this community. I hope to be received and responded to, as such <3