Hi ,
From my experience the kind of relationships you have in school,we expect it to be ideal.We meet this one person who matches with the characteristics that we have formed in our mind and then we perceive the person to be ideal.Yes it feels a bit shattering when someone you have chosen to give your everything chooses not be part of your life.But the most important mistake we make is start idolising them like their smile or way of talking that attracted us to them.What you need to do is stop romanticising and deal with the reality.You probably attracted him because you were full of life,full of love,ready to fall in love with a special person.I think you should connect with your inner self again and be that person again so that you can attract again a special someone.
Lots of love and warmth.

Hi ,
The fact that you have taken the decision to move on and be indifferent is job half done.I too was in a relationship 6 years ago and it was kind of intense and it was a tough breakup.We have all this ideal situations and images in our head when we are in love and when those are shattered it is difficult to move on.What I would suggest that helped me would be practice mindfulness and love kindness meditation.Start asking yourself questions like why do I think about him?Is he the only person in the world that makes me happy?These questions will help you to become indifferent to him and start wishing well in your mind.This will help you not have any grudges against him. Wish you all the best and have a great life.