[header] How to deal with an ex best friend [title] Find closure. [step] When your friendship ends, it is important that you accept that and resolve your feelings. You can write a letter to your friend expressing all of your feelings (you don't have to send it to them), or you can create a ritual to symbolize the end of the friendship. 
To be happy, you will need to acknowledge the your feelings, process them, and move on to the next stage of your life. [substeps] In your letter, you might write about how the friendship started off great, but then went downhill.