Answer:
Sample:
Dear [Friend's Name],
I hope this letter finds you in good spirits. I am writing to apologize for the mistake I made [insert specific mistake]. I understand that my actions caused you harm and for that, I am truly sorry.
I want you to know that my intentions were never to hurt you, but I understand now that my actions had that effect. I have thought a lot about what I did and I have realized that I was wrong.
I value our friendship greatly and I would be devastated if my mistake caused any permanent damage to our relationship. I hope that you can find it in your heart to forgive me and give me the chance to make it up to you.
Once again, I am deeply sorry for what I did and I hope that we can move past this and continue our friendship.
Sincerely,
[Your Name]