Draco was sitting at home, drinking himself into an early grave as he stared into the fireplace before him. He didn't bother to light it; he never did. On particularly bad days like this one, he knew he would stop noticing after the third or forth drink. Nothing could possibly make him colder than the last memory he had of her.
He told himself to look away, to shut out her screams and ignore the way her body contorted in agony, but he couldn't bring himself to do it. She needed him to stay; she needed someone else to feel her pain as though it was their own. She needed him most in a time where there was nothing he could do but stare into her eyes, silently trying to tell her that she was not alone. He promised her that once, that he'd never leave her, but he doubted this was the scenario she had in mind when she'd asked.
At this particular moment, if he so much as moved a muscle, they'd both be dead. If he managed to stay perfectly still, emotionless and stoic, Bellatrix would eventually tire of her and have him take her down to the dungeons with the rest of them. Either that, or Potter and Weasley would find a way to help her without getting her killed; they always did. He could suffer for a few more minutes, if it meant she would live.
But when the dagger came out, Draco could handle no more. The tears in his eyes were about to spill over, and he was blinded with rage. He managed to take just a single step forward as Bellatrix began carving into Hermione's flesh before his mother wrapped her hand firmly around his wrist, her eyes pleading with him not to move. Looking back at Hermione, he saw her body arch in pain as another scream ripped from her throat, but she managed to stay collected enough to shake her head ever so slightly, forcing him to comply. They wanted him to stand idly by while she was broken on the floor, and he didn't have any other choice.
She wasn't supposed to die that night. Potter and Weasley were supposed to rescue her. Bellatrix was supposed to stop after she carved the word "Mudblood" into Hermione's flesh. He was supposed to save her. But nothing that was supposed to happen that night did, and ten years later, Draco still couldn't rid himself of the moment when her eyes glazed over, a final tear rolled down her cheek, and he watched the only woman he'd ever loved die on the floor of his own parlor.