I have a feeling that my partner is not my original partner

I don't know how to explain this but I can't shake off the feeling. My fiance, let's call her Amanda. We've known each other since grade school. We have pictures of us being friends since grade school. Long story short, Amanda became my fiance by the end of 2022. And we were supposed to get married in 2024 but we've called off the engagement. I could tell she was relieved when I told her. We took a break, that turned into weeks that turned into months. We only broke up for like 3 months but this whole time, I couldn't shake off this feeling that she's a completely different person or that she's not the same person I was supposed to marry. But then again, we've known each other since grade school, right? It's all weird and it's like, Amanda visiting my parents for the first time even though she knows them. Amanda not knowing simple things about me. It's all in my head, right?