A/N I couldn't believe that she did that, I couldn't believe that it was him who did it, thus I've tried to explain it away. Spoilers for HBP.
He collapsed in the cold wet grass, not wanting to move. He never wanted to move again. He was ready to give up the fight, a fight he didn't want to continue any longer not after what he had been forced to do. A fight that was no longer worth it, his only motivation was gone, betrayed by the one who had thought him worthy of salvation, the only one to take him in, shelter him, protect him.
And now the man who had vowed to protect him was gone, slaughtered at his own hand. He lifted his head long enough to gaze and the gloved hands. He couldn't stand the site of them, Lady MacBeth knew far too well how hard it was to wash away the bloody that you have spilt. He could see it all there, but most vividly the bright red of the most recent, a death that he should have prevented, not caused.
But he had to. He thought he had, at least, at the moment, with all those around him, he knew he had to, that he had no other choice, but looking back on it, it was the worst mistake that he had ever made in the few pitiful years of his existence. The only person to have ever fully trusted him was gone, and it was all thanks to him and one moment of misjudgment.
He hadn't known what possessed him to do it, besides a sudden, overwhelming urge and the words were on his lips, and the bolt of green light had echoed through the room. He felt the bile rising in his mouth and rolled onto his back, purposely, hoping to end the bitter existence that he knew was left. There was nothing left for him any more. Two words, six syllables had taken away the only thing that had meant anything to him, the only one who thought that he was not yet past salvation.
And he had failed him.