How do I tell my dearest friend I'm a CD?

Tell her before you actually CD in front of her, else it'll be a big shock and she might react badly. If she already suspects something she'll really appreciate you telling her. Also make sure you tell her in person. I'm just judging from how I'd react if it was one of my friends that told me, i'd be fine with it but i'd rather hear it and then see it than see it and then hear it.