If someone shares another person’s private pain with you, you’re not being trusted. You’re being recruited.

Hearing somebody else’s private trouble secondhand means a line already got crossed. The person telling you is not confiding, they are enlisting: once you know, you are inside the story and expected to take a view, and the person whose pain it is was never asked. Dressing it up as concern is the usual move. The test is whether the subject would be comfortable hearing it repeated.

You can stop it without a confrontation: say you would rather hear it from them, or change the subject and skip the follow-up question. Then do not pass it on. Being a dead end for other people’s private business is a real service.