Everyone has black desires, and everyone has a "dark moon" in their heart. The moon is the shadow of the sun, and the dark moon is the shadow of the soul, representing the parts of ourselves that we are afraid to admit and face.
"Even if I stand in the crowd with a smile as bright as the sun, there is always a shadow behind me, dark and cold. I turn my head, but I can't see it. Is it hiding from me or am I hiding from it..."
Afraid to admit it because it is black, afraid to face it because I am afraid that I will be controlled by it. But when you are sad, when you are helpless, when the last bit of light is extinguished, when you hate your own existence, the "dark moon" will emerge from its black lair and engulf everything with its black shadow...