How did you get over someone you once loved?

My boyfriend and I just broke up. It was mutual because we realized we both just weren't that happy and that we had too many fatal differences. We were dating for 4 months but we were best friends for a year before. He said he still wants to be best friends but I am so heartbroken. He was my first everything and my feelings for him are so strong. I am going to miss being in a relationship with him even though I know it's for the best. He's been understanding and has listened to me tell him how I feel but I just can't bring myself to imagine being as comfortable as I am with him with someone else. How did you get over someone you once loved and move on? Because I am having the toughest time.