Though they like the drama, they take this seriously and would rather lie on a bed of nails than violate a promise or ruin their trustworthiness.
Telling a Capricorn your secret will keep it hidden until you forget it.
Because they're so moral, they know sharing what you trusted them is proper. They'll tell you if they disagree with your ideas but won't tell anybody else.
Libras are reliable and will keep your secrets till the end to preserve social order.
They're also emotionally motivated and compassionate, so if this secret is sad, you'll have a listening ear and a shoulder to weep on.
Due to this, you may reveal more than planned. Pisces keep secrets no matter what. They love you and know you would love them.