OP, I'm sorry that you are hurting over the loss of this friendship. It does happen that friends grow apart.
In my case I was part of a small group of 'best' friends at uni. We were close like sisters, but I had one friend where it felt slightly more strained than the others. We had been drawn to other members of the group but not especially to each other. Nonetheless we spoke all the time, were super close. I loved her.
In our early 30s, after over a decade of very close friendship, with all life's ups and downs, she behaved very badly to me - told very hurtful lies behind my back to our other friends. I called her out on it and she defended herself, claimed it was 'a version of the truth', didn't apologise. I just knew in that moment that she wasn't my friend any more.
It's been a decade and although I've had moments where I've thought about reaching out, on the whole I think we'd just grown apart and weren't compatible as friends as adults like we had been when we were much younger.
I think like any relationship, with time you do get to the point where you can remember the good times without it causing any pain that they're not in your life any more. Hope you find your way to feeling peace about it.