Why is it so tough to move on?

I broke up with my girlfriend a few months ago. I initiated the break up because I was scared and didn't want to hurt her in future, idk what was going on in my mind. But then I started missing her, a lot. It's been a month, I cry at night, I can't focus on my work properly. Everything reminds me of her. I used to live 2hr away from her, but now it's just 20 mins, but I can never see her again.

In every 1 2 days I feel like i'm getting over my break up, but then randomly something hits and i'm back at square 1. I think I really want her back but I'm not sure if she even has any feelings for me now.

also I'm not sure if we have a permanent future together, It can be my lonelyness but I'm not sure.

How to get over her? I can't live like this😭