Hi Nik,
I'm new to the forum as of today and couldn't help but reply b/c I can relate. Though the calls might've stopped the thoughts haven't because he still lingers in your heart. What I found useful was writing down the reasons why I still thought about that person and reasons why I need to let go. Afterward, I prayed for forgiveness for myself and for him. Soon I felt him leave little by little from the grasp he had on my heart. He'll always be there in your heart because it was a relationship that meant something to you. But its taking back your power over the relationship that makes it easier for those feelings to pass. Continue to pray and talk to God for strength and guidance and talk to a non-judgemental ear if you need to vent...that helps as well.
Sorry if the advice wasn't better but I know the path you're walking on..it does get better.