If you're a confidante, two things must be true: you have to be female, and you must be someone who people feel comfortable telling secrets to.
If you have a confidante, you're lucky. She is a friend you can confide in, someone you trust with your private thoughts, and who you're sure can keep a secret. If your trusted friend is male, you call him your confidant. In fact, you could call a male or a female "secret keeper" your confidant (without the "e"). Both versions of the word come from the same root as confident — which you can trace back to the Latin word meaning "to trust or confide," confidentem.