Evergreen.

Severus Snape wasn't always that way, you know.
He wasn't as consumed by hate, depression and impotent rage. Once he was light, not dark.
He came to my school aged eleven. A thin, pale wide-eyed boy with too many bruises and with knowledge of curses beyond his years.
His father, Balthazar Snape was a Slytherin, his mother, Ariadne, a Ravenclaw. Who do you think gave young Severus his nightmares, his bruises, his unnatural knowledge of all things dark? It's not who you think.
Severus wanted to help, at first. He said to me that ambition isn't necessarily a bad thing, that because he was Slytherin, it didn't mean he was evil. He was twelve at the time. He would repeat the same thing three years later, but with less conviction after the beating he had received by Black and his friends because Severus had been talking with Lily Evans, James Potter's girlfriend, and Sirius took offence. It would be Sirius's violent temper that was to be his eventual downfall. However, this is not Sirius's obituary speech I am writing.
I am not making excuses for Severus; he was never easy to get on with, even as a child. He was quiet, introverted and prone to bouts of depression. Some quite violent and destructive bouts at that. Poppy still remembers the emaciated and broken body we found in the Forbidden Forest after he had holed himself up in a cave for several weeks, claiming he wanted to end the suffering. It was the toll of his mother's constant berating and the constant threat of beatings from Sirius that broke Severus. I always believed that Severus went to Voldemort because of the lack of family he had, but he wasn't evil. He came back to me, a hysterical wreck of a twenty-one year old begging forgiveness at what he had done, claiming he could still hear the screams and see the blood on his hands, pleading with me not to send him to Azkaban.
I gave him a second chance. He became one of the school's youngest Professor's dealing with the subject he excelled at most - Potions. Fudge declared, in his infinite wisdom, that Severus become a spy, a test of his faithfulness. He never believed a Slytherin could be good.
Severus in the mean time built a wall to hold in everything that had happen and would happen. He closed himself off from everyone, except me, his Saviour. I am not sure I was that. I blame myself for what made him that bitter, twisted man.
He hated Harry. That is an undisputed fact. It brought back too many memories of his childhood, something he would rather forget. It's ironic then, that Severus died to save Harry. He took the curse meant for Harry, writhed in agony and then died.
A life borne of pain to end the same way.
Severus wasn't always that way. I was still waiting for him to bloom again and gain life, but I was too late.