Rebuild the missing context
Assume the recipient will not remember every date, promise, or earlier conversation. For a message about how to decline a date without leading someone on, use this factual base: acknowledge what was requested, any real timing issue, and whether your answer applies only now or more broadly.
Say what needs to happen next
State the decision, information, or practical action you need and include a real deadline only when one exists. Give a direct no, a limited alternative only if you mean it, and any practical information they still need. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Avoid making urgency into pressure
Do not overexplain private details, blame another person, or say maybe when the answer is no. When pressure, coercion, or retaliation is possible, use a safer channel and involve appropriate support. Do not make the other person responsible for reducing the discomfort that prompted you to write.