Note: This uses characters from a different fic by me, Slytherin, Through and Through. Should be fine without having read it but will probably make more sense with it.
PROOF
I wanted to stay. This was what I told myself as my legs seemed to stand up of their own accord and began taking me, slowly, out of the Great Hall. I wanted to stay, but I couldn't. I was four days off my seventeenth birthday. They wouldn't have let me.
Somewhere deeper inside me I knew this was just a sickening, pathetic excuse, that in reality the thought of fighting Death Eaters, Death Eaters, for fuck's sake, would have terrified me into a quivering mess of bones and flesh and skin. But I still would have done it, if I hadn't had my weak excuse. Or maybe I wouldn't. I don't know. I don't like thinking about it.
I glanced quickly at the Slytherins around me. Alexis cast a derisive look backwards at the other Houses as she walked purposefully out. Nate stared at the floor. Of course, there was no question of whether he would stay or not. He probably would have ended up duelling with his own father. Daphne's legs were shaking as she moved away. There was a horrible feeling of shame around us that you could almost see.
Turning to cast one final look over the Great Hall as I reached the door, I saw that not one fellow Slytherin had stayed to fight. It made me feel sick, because we'd just proved to all the smug ones sitting waiting to give up their lives what a load of base, pathetic, cowardly creatures we were. And I was part of that problem. I could have stayed. But I chose not to.
My eyes hit the Gryffindor table, just as it went out of sight. To my horror, I saw my little sister sitting resolutely. She was only just fifteen. I wanted to run back in, grab her arm and pull her with my to safety but my legs wouldn't do it. I wanted to get away from that Great Hall as fast as possible. It would always be the moment that I'd try to forget, the time when I'd neatly proven to everyone that I was exactly what they'd always assumed me to be.