What does it really mean when someone says they have a secret?

What does it mean when they tell you have a secret, then ask you whether they can trust you. Then you respond with an assuring comment, hoping it will encourage the telling of the secret.

Nobody to tell, you say.

And he responds, you have the entire world to tell. your journal. your blog.

Then the secret-teller withdraws. And you realize that you might have said the wrong thing. And the secret is left shrouded in darkness.

Then it bothers you for days thereafter. Because it was something that he wanted you to know, but he had changed his mind at the last minute.