I am writing to apologize for my recent violation of [describe the violation]. I understand that my actions were inexcusable and I accept full responsibility.
First, I want to apologize for the distress and inconvenience that my behavior caused you. I understand that you had every right to expect better from me, and I regret that I let you down.
Second, I want to apologize for the impact that my actions had on our relationship. I know that I have broken your trust, and I am deeply sorry for that. I am committed to rebuilding that trust and to being a better friend in the future.
Finally, I want to apologize for not being more mindful of the consequences of my actions. I understand now that my behavior was inappropriate and that it could have had serious repercussions. I am committed to making better decisions in the future.
I understand that an apology alone is not enough to make up for my mistake. I am committed to taking the necessary steps to make sure that something like this does not happen again. I am willing to do whatever it takes to make amends and to regain your trust.
Once again, I apologize for my behavior and I am committed to being a better friend in the future.