As a death eater and Voldemorts right hand man he had to do something that he regretted already. He had to kill you, his lover. Voldemort thought you were a part of the order, when in reality you were just an innocent Hogwarts Student with outstanding grades. You were awoken by the footsteps of Severus as he snuck into your dorm, you saw him standing over your bed, his wand in hand as he slightly trembled, even behind that mask is a single tear falling from his eyes