How to deal with seeing my ex everyday

I miss him so much.He was best friend and first love but stuff happens and he decided he didn't want me in his life.Its been hard but I'm finally ready to let him go and move on,even if a part of me still loves him.But it's so frustrating because I have to go to school everyday and see him.Most of the day he's close,not because I try to stay close,but most of our classes are together.It just hurts so much to see him happy, it makes me feel like he never cared.I want to move forward and forget,but seeing him all the time makes it extremely painful and difficult.Idk just am asking for any advice.