A middah tovah limaalah is never to reveal private information about another person unless they tell you go and say. To the point that Moshe Rabbeinu would not have given us the Torah but for the fact that Hashem told him to.
But, we for the most part are not at that point. Therefore, use indicators to judge if you can reveal the information and the stronger indicator when contradicotry indicators present. For example, your friend stands in front of you and tells everyone passing by information and to keep it quiet; you need to decide which indicator is stronger.