We Used to Like Eachother and Now She Wants to Be Friends?

Hello everyone! I (23M) have been talking on and off with a girl (21F). We first talked because she was interested in me. We got closer and were basically "dating" but didn't do anything special except kiss. After some time, she said she did not want a relationship and wanted to work on herself, which I respect, so I said let's not talk. Then, it was just a bunch of on and off talking between us. Fast forward half a year, and she just wants to be friends.

I still hold feelings for her, and I think she just moved on. I like her company and as a friend, but I also like her in a romantic way. I know I am just going to back away now because I am tired of this mind fuck. But, it's so hard because I thought we'd be imperfectly perfect for each other, and I don't know if I can ever fully move on from her. I can't imagine myself with another girl. I guess my question is… how do you move on from someone you never really dated? It's so hard for me because there was nothing wrong between us, except timing unfortunately, and I can't really tell myself "Oh, we didn't work out because of [personality differences, constant fighting, etc.]" like my past relationships.