Confiding in someone means that the person confiding is sharing something personal and private with the confidant in the expectation of that something being kept private. It is an act of trust. The confidant betrays all trust if she/he then passes that information on to others, except in very rare circumstances, such as an admission of criminal guilt.
Should I be diagnosed with a terminal condition, there are those I do not wish to know at all until I have died. There is no one I wish to know immediately, someone in whom I should like to confide a bit further down the line, and some with whom that confidante may herself confide as appropriate (inn my opinion), again, later down the line. Hypothetical, so I might change my mind, but I would certainly expect confidences to be kept confidential.