Severus had never been pure. His thoughts, his wants, even his blood… polluted. Shunned for all of these reasons, he'd never bothered to pay any mind to the people around him. Until he met her. Soon she was the only thing he could think about.
But she wasn't like him, which made his hunger for her increase intensely. He wanted to spoil her, rid her of all innocence and make her ever so slightly like him.
Touching, kissing, fucking… would do nothing. The same blood would run through her veins and she would eventually forget him. He couldn't mark her.