Say the boundary in operational terms
Name the contact, behavior, topic, access, or commitment you will and will not participate in. For a message about how to support a family during military deployment, use this factual base: use the person's language for the transition and notice the immediate access, identity, housing, work, or family need.
Define any necessary exception
If an exception is necessary, give it one purpose, one channel, and a clear limit. Offer one concrete step and let the person decide whether they want problem-solving, company, or quiet. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Respond to escalation safely
Do not demand optimism, a complete explanation, or a timetable for adjusting. Use qualified legal, medical, trauma, housing, immigration, or emergency support when the transition carries serious risk. You do not need the other person to agree with a boundary for you to follow it consistently.