B'cos now what u all busy with is thinking of him and everything form the past.
I recommend u find sth just to keep u busy with like studying, shopping, making DIY stuffs, cooking, hanging our with bff whatever. I always writing thesis when I can't make up my mind. It always takes all of my time and keep my busy even in my dream.
if u can do that at least for 2 weeks, 50% of ur feeling for him will go and if u can just do it for a month, 99% will go. After that u just get going.
It won't be difficult. Just find sth u love to do and u can do it well to keep u busy. Always works.