Author's Note: Oh dear. Poetry. You have no idea the amount of courage (and chocolate and tea) that it took me to put this on here.
I'll admit it was inspired by the Half-Blood Prince movie, particularly the images of Snape, Draco and the rest of the Death-Eaters walking out of Hogwarts. Perhaps more particularly, it was inspired by the deleted scene "Clouds Gather as Flitwick Conducts Orchestra" in terms of Snape's feelings.
In Order of the Phoenix I believe Firenze mentions something about Mars being the bringer of battle.
Bringer of Battle
I leave, walk out of the castle,
Dark robes flapping behind me.
Mars shines bright tonight.
*
The Dark Mark also burns in the sky,
Brighter than the moon,
Illuminating the gates to which I flee.
*
Potter's boy, Lily's boy, shouts behind me,
Angry, hurt, grieving,
Hating me more for my newest sin.
*
Two words, all it took.
A protector gone forever,
The world plunged into darkness.
*
My fault, all my fault.
The boy is right to rage.
But for me, Albus would be here a while longer.
*
I have a duty,
One more before the end,
To keep the boy alive, for a time.
*
So I spit angry words, vitriol and spite,
Hate as well, but not for the boy,
This hate is for someone else entirely.
*
For myself, the place where this tale begins,
Alone, confused, and scared,
Begging for forgiveness.
*
Years spent in servitude,
Two masters, one "Light" one "Dark"
Equally manipulative.
*
Forced from my home,
Scared away by a boy with too-green eyes
And the memory of my mistakes.
*
A man, falling, falling, falling.
A man, carrying out a bitter promise.
A boy, facing his demise.
*
Moving forward alone
For the memory of a lost love,
Gone.