Reign of Insanily

As Harry continues to spend more time with Bellatrix, he's lost all sanity, slipping into her level of insanity. However, only they both know the darker side of him. But what happens when he starts Marking everyone at add times during the day? How is it that he's suddenly more darker than the Dark Lord himself? And why is Bellatrix so determined to have him? Dark/Insane/Powerful HP