I'm sorry I could not be of more help, but I recently went through something similiar to this after being diagnosed with Bipolar a month ago. My best friend, who had always seemed very trustworthy seemed to think that my "illness" required "recovery" and that she would interfere with this so-called recovery. Needless to say, we haven't been talking much since. She is your best friend, however, and if you feel like there is an elephant in the room by you not telling her, I would advise you to go ahead and do it.