The person who confided in you did not give the whole group permission to know.

Confidences are granted individually and travel collectively. Something told to you in a kitchen gets repeated to one trusted person, who repeats it to another, and each step feels small while the total is a private situation circulating among people the teller never chose. They usually find out through a stranger’s sympathy, which is a particular kind of exposure.

Treat the boundary as one person wide unless you were told otherwise. If passing it on seems necessary, ask them first, and accept a no without needing a reason for it.