Nostalgia is killing me

Yesterday, I completely broke down crying in my bed, before sleeping. Some time ago, I found my old books from previous grades and I seem to have been just stuck on that. I keep thinking about 1st and 2nd grade of high school (in 3rd rn) and I get a bittersweet and weird feeling about it. I wasn’t miserable in the previous grades, but I definitely wasn’t the happiest and I realised that a long time ago, but again, I seem to be stuck reminiscing about it. I’ve already tried to tell myself, that I’m still living through the high school experience, but it just doesn’t seem to go away. When I stopped crying yesterday, I went on tt and it played Katy Perry’s „The One That Got Away” mashed up with itself, so the very beginning playing over the outro/bridge and it made me spiral again. (Not sure why my brain works that way though). Every time I have a nice moments whether it’s with my classmates or family, the memories just seem to return for some reason. Any advice to stop thinking about or get over that is welcome. Thanks for reading