How to get over someone?

How do I get over someone I never really dated? We made out causally and did all the relationship stuff (sleepovers, cuddling, holding hands etc) and I have truly never felt safer and happier than when I was with him. I think I overestimated how much he was into me and was acting a bit too much too fast and he ended up losing feelings and ending things. He seems to be fine and I just can’t get over him and wish everything could go back to the way that it was. we live in the same uni res and I have to see him everyday but it’s been 3 weeks and my feelings haven’t changed at all. I need advice cuz I feel like the pain in my chest is never gunna go away