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.