Dear [Friend's Name],

I am writing to you to apologize for my behavior recently. I realize that I have not been the best friend to you and that I have let you down. I am truly sorry for any hurt or disappointment I may have caused.

I value our friendship and I want to make things right. Please know that I am taking responsibility for my actions and I am committed to being a better friend to you in the future.

I hope you can find it in your heart to forgive me and give me another chance. I miss our friendship and I would be devastated if I lost you as a friend.

Once again, I am sorry and I hope we can move past this.

Sincerely,
[Your Name]