Recognize what makes this moment difficult
Acknowledge the event directly without turning it into a lesson, comparison, prediction, or silver lining. For a message about how to set a boundary around constant friend venting, use this factual base: name the recurring contact, request, topic, or behavior and the effect it has on you.
Offer support that can be accepted
Offer one specific form of practical or emotional support and make clear that no immediate reply is needed. 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.
Follow their pace rather than yours
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. The recipient decides whether they want conversation, ordinary company, practical help, professional support, or quiet.