To whom you betray your secret you sell your liberty.

A secret handed over does not stay yours. It becomes something another person holds, and holding it gives them a small permanent claim on how you behave around them. You will find yourself managing that relationship differently, watching your footing, keeping them content. None of this requires any bad intent on their part, since the constraint comes simply from the fact that they know.

Before telling someone something you would not want repeated, ask whether you are willing to be a little less free with them from now on. Some people are worth that, and telling them is how trust gets built. Decide which kind this is before you speak.