Playing the impartial role is Libra's forte. You might not initially believe that the people represented by the scales, who are interested in issues of justice and fairness, would make ideal secret keepers because it looks like they would not approve of gossip.
But it's precisely that sense of fairness that makes them so incredibly deserving of your faith. They might not be the biggest fans of gossip from a moral perspective, but they will be ready to listen to you vent if you have something you want to talk about.
Contrary to Libras, Capricorns adore rumors. Some enjoy it because it keeps them more informed, gives them a clearer picture of what their pals are up to, and enables them to construct a red-string theory board in their thoughts. Others enjoy it because it allows them to remain aloof from drama that won't directly effect them.
A Pisces will keep a secret not simply out of common courtesy but also because they truly, really love your connection if you are close enough to share such intimate details. They're willing to do whatever to strengthen your relationship, including keeping any secrets you choose to divulge.
Because they don't want to lose you or see you suffer, especially by their own acts, Pisces will avoid anything that could endanger your relationship to the farthest extent.