Confidentiality is respect for information that trusted you before it trusted anyone else.

When someone tells you something difficult, they are handing over something that was previously theirs alone. Repeating it, even lightly, even to one person, changes what it was. Confidentiality is not a formal rule so much as an acknowledgment of what was actually given. Most people who break it do so casually rather than maliciously, which is what makes it so common.

Treat anything told to you in confidence as unavailable, including in the version where you leave out the name. If you are unsure, ask whether you may mention it. Being reliably closed with information is a rarer quality than it should be.