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 resolve conflict over a borrowed item, use this factual base: use one or two recent examples and name the trust, effort, money, or inclusion issue they created.
Offer a proportionate next step
Match the size of the request to the relationship and to what the recipient can reasonably decide now. Ask how your friend understood the situation and propose one change that can be tested. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Protect privacy on both sides
Do not assemble mutual friends, post indirect messages, or use confidential information as evidence. Stop direct contact and use appropriate support when there are threats, stalking, coercion, or safety concerns. Use the most private legitimate channel available and do not share the exchange to recruit support or pressure.