When a friend tells you about their crush, that info is not group property.

Something told to you quietly was handed to you, not to the group chat. The temptation is real, because knowing a thing other people do not know is a small kind of status, and passing it on spends that status all at once. What gets lost is bigger than the secret. Your friend learns what happens to the things they tell you, and they adjust.

Default to silence unless they say otherwise. If you are not sure whether something was private, it was. And if you already let one slip, say so to them directly before they hear it from somebody else.