[Here briefly describe on Sample letter to your friend for apologizing for your bad behavior, misunderstanding, or not attending party etc. You can Write this letter via Email to him apologizing for your behavior. You can modify this format as your requirement.]
Apology Letter to Friend after Bad Behavior
I hope you are doing fine. I am writing this letter to you with a very heavy heart. It is because I am very sad and sorry about my behavior with you the other day. (show actual problem and situation). You are my best friend and I love you from the core of my heart and I am sure you know that. I want to apologize to you and I will feel sad and depressed until you write back to me accepting my apology. I request and I know that you will accept my apology.