Disclaimer: I do not own Harry Potter.
By Silver Sailor Ganymede
The guilt is always there on some level, a whisper in the back of his mind berating him for his past foolishness. Tonight it is worse though; it screams at him rather than whispering, gnawing and tearing at his soul and asking him how he could ever have been so foolish.
He tells himself that he was young and stupid, and every young, stupid wizard tries to invent spells at some point. While that's partially true, he knows that not everyone tries to invent dark curses as a teenager. Severus Snape was the only Slytherin malicious enough to do that, to invent curses and to scribble them, along with the words 'for enemies' in the margins of his Potions textbook. He was an idiot enough to do that then and he is paying the price for it now.
That spell had been meant for enemies – made, Severus remembers, with the intention of slashing James Potter in two once he found out that he had stolen his precious Lily from him. It had not been meant for use on his students, and certainly not for Draco, who had already been so pale when Severus had found them that he had thought the boy was dead. He isn't dead though, just slowly breaking under the pressure of his mission. Draco is even more broken now that Potter has had his way.
What hurts Severus the most, though it takes him a long time to finally acknowledge it, is the fact that it was Lily's eyes that were glaring maliciously at Draco's prone body on the floor. Had it been James Potter's eyes then Severus would not have been surprised, but Harry has his mother's eyes, and all Severus can think about now is that fact that he has failed to protect Lily's son from the darkness that magic can create. He promised to protect the boy a long time ago and he hasn't even been able to do that correctly.
For the first time, Severus has realised that Harry is truly Lily's son, and the guilt caused by his failure is eating him alive.