Professor Snape vented his hatred on you because your father stole the person he loved, namely your mother. He always punished and sometimes even tortured you until the end he poisoned and almost killed you, but he realized that because to him you were just a child who didn't know about your parents' problems with Severus Snape. After Severus Snape almost killed you, he became an overprotective person. he even considers you his own daughter and always calls you 'my little princess' or 'cutie pie