Why does moving on feel so impossible? How long does it take?

I met this guy and dated him over the summer. I have never had such strong feelings for someone. We had to go away to different colleges at the end of summer but still kept in touch. After the first semester, he was graduating but I was still in my second year. We saw eachother again over holiday break but I had pretty bad anxiety that day so I was really quiet around him. After that, we were supposed to hang out again but I could feel something was different. I knew this was probably the end. So I reached out to him and asked him how he was feeling because if we weren't on the same page I had to move on since it had been so long. I didn't want to waste my time. He said he didn't want any relationship right now at all and it was too hard because I was away at school and he was starting his career. I was crushed when he said this but I understood. I knew he just didn't want to date me because he just didn't have as strong feelings for me as I did for him. He still wanted to be friends and even tried to see me again but I told him no and said it was too hard for me. I told him to let me move on and maybe after a few months we could be friends again. So the day all this happened, of course I was upset but after that I felt nothing. I almost felt like I didn't care. I wondered if I was in shock because how could I have cared for him so much and not be hurt when it ended. I did think about him but I just distracted myself with other guys, dating apps, or talking to friends. Then, I was driving back up to school one day and got in a car accident. Right after the car accident, I also got a text from him. After that I broke down and all of it started to hit me. Now I am home again for spring break and I can't stop thinking about him or getting flashbacks. It hurts so bad. I was definitley in shock at first. I miss him so much and part of me wishes we still were friends or that I could see him but that would hurt because I don't just want to be friends. It just feels so impossible to move on from him. I've never felt this way about someone and I'm mad at myself because I was so sure I'd be over it by now. It's also hard because I've been friends with his sister before I even met him so she reminds me of him too. I wish I could reach out to him but I know it'll go against what I told him and ugh. I really thought we were meant to end up together too. It's probably bad to reach out, right? I don't know what to do... how long does it take to move on from people? I know "time heals everything" and all that. I just wish I could move on from him more than anything so I don't feel this way anymore. How do you move on when it feels impossible?