Write from facts rather than momentum
Pause long enough to remove accusations, assumptions, and details that belong to someone else. For a message about how to address a friend who cancels every plan, use this factual base: name the recurring contact, request, topic, or behavior and the effect it has on you.
Offer a proportionate next step
Match the size of the request to the relationship and to what the recipient can reasonably decide now. 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.
Protect privacy on both sides
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. Use the most private legitimate channel available and do not share the exchange to recruit support or pressure.