How Do We Stop Obsessively Thinking of Someone?

In this video, Intimacy expert Allana Pratt gives tips on how to stop obsessively thinking of someone
Q: My now ex best friend and I had a fallout. It’s happened before but this time it's serious. She’s so mean to me and we don’t bond anymore but I still miss her. She’s done this to me multiple time and I don’t know what to do. She only comes to me when she needs something and I feel so used. Today she said a lot of hurtful things. I guess my question is: Why do I miss someone I no longer want to have in my life?