Your friend told you who they like. That name goes in the vault and never comes out.

Being trusted with something small is still being trusted, and this particular kind of information is socially expensive to hold and very cheap to spend. That is exactly what makes holding it mean something. The moment it moves, you have converted somebody’s vulnerability into currency. There is no version of this where they fail to work out what happened.

Keep it, including from the person you tell everything to. If somebody asks directly, say you do not know. Being the person things stop with is a quiet reputation worth having.