I have never revealed my 'darkest secrets' to anyone. I'm careful enough to understand that once they are out, there's no way they are coming back. So yeah, I don't trust anyone enough to let them in on those secrets. If anything I've told anyone is ever revealed, then it's not much of a big deal to me because I wanted them to know in the first place.
But if I were to face such situation (back-stabbed in a ploy schemed by the said close friend), I would bring out my inner bitch. Throwing sarcasm and dropping acidic hints like some sort of passive-aggressive wreck while ACTUALLY confronting them. Yes, being all indirect and cryptic about my emotional state yet frontal about the problem at the same time. This would go on for some brief time before I reached the "goddammit-this-is-not-right" phase. By then, I would act and think less emotionally and more rationally. Time to grow out of the attachment and learn to face things head-on. Talk over the problem with the aforementioned person and solve it while still keeping my head because I'm one peace-loving person.
But if the culprit decided to act all innocent and douchebag-y about it, then adios, "amigo". Jerk face doesn't deserve my love :)