I kept things a secret, too. For a long time. Why? I guess because I was 'ashamed'...but also because I knew my exah would be sssoooo angry if anyone were to know what was really going on with him. He used to tell me that this was a private family matter and I believed him...until I couldn't handle things on my own anymore.
Addicts thive on secrecy and deception. If a spot light is shone on their problem, they lose the ability to lie, manipulate, and use people around them. Its no wonder they want us to keep their secret.