I too beneath your moon, almighty Sex,
Go forth at nightfall crying like a cat,
Leaving the lofty tower I laboured at
For birds to foul and boys and girls to vex
With tittering chalk; and you, and the long necks
Of neighbours sitting where their mothers sat
Are well aware of shadowy this and that
In me, that's neither noble nor complex.
Such as I am, however, I have brought
To what it is, this tower; it is my own;
Everyone has a dark side. Yours might be more obvious to others than you think. 
 Swiss psychiatrist  Carl Jung  thought all human beings have a thing called a  Shadow  that’s basically a confused, anxious unconscious side, “the dark side of your being”. It’s likely Millay’s making a subtle reference to her amoral, secretive sexual side. 

I Too Beneath Your Moon Almighty Sex