Make room for the other version
Ask what the other person understood before assuming that you are arguing about the same facts. For a message about how to set a boundary around keeping secrets, use this factual base: name the recurring contact, request, topic, or behavior and the effect it has on you.
Correct the record precisely
Correct only what you can support, acknowledge any real impact, and propose a practical way to prevent repetition. State the limit, any acceptable alternative, and what you will do if the pattern continues. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Agree on a testable next step
Do not diagnose your friend, list every past grievance, or threaten public embarrassment. For stalking, threats, coercion, or self-harm concerns, preserve evidence and use appropriate crisis or safety support. Do not recruit an audience, publish private evidence, or turn a misunderstanding into a campaign about character.