He was spiraling.
Spiraling, like he always was lately.
Except this time, he knew there was no coming back if he let himself spiral out.
His whole life he'd been fighting the darker impulses his father kept trying to instill in him. Sure, he was a prick sometimes, but he wasn't his father. He hadn't let his cowardice bring him into that dark storm that had trapped Lucius.
As he looked at Dumbledore, though, the fear that usually swept him closer to the storm threatened. His wand was still pointed at Dumbledore, as it had been for a few minutes. Fear of being caught in the storm for good stayed his hand. Fear of dying motivated it. Contradictions, swirling around and colliding, moving him like a rag doll between them. He couldn't live like this much longer, constantly exposed to the storm. He wasn't strong enough. He would either buckle under the weight of trying to stand his ground or be turned into something he knew he wasn't; not really.
He wished, for the thousandth time that term, that children could choose their parents. That he could have been raised by someone who actually taught good things. He had respected his father all throughout childhood, but that respect petered out as Draco approached seventeen. As his father handed him over to the Dark Lord like a dog. Draco had seen Lucius quail under the Dark Lord's presence alone, which had confirmed a suspicion he'd had: Lucius was a coward.
Draco knew he'd gotten it from somewhere, but he'd assumed it was his mother.
Lucius taught Draco how to be the worst kind of coward: one who acted brave until the very moment bravery was needed. If Draco had had any bravery at all, he would have told his father he didn't want to be a Death Eater. He would have told Crabbe and Goyle that he didn't want anyone to die.
He would have told anyone who would listen that he was scared.
That was the one thing he never seemed to go long without thinking: he was scared. Scared he wouldn't be a talented wizard. Scared he would disappoint his father. Scared his friends would turn on him the instant they found a more powerful person to follow, and he would be alone; or worse: scared that he already was alone. He'd always managed to hide the fear, with a boastful swagger and step, pretending to be his father. He'd parroted his father's words so often he could barely distinguish them from his own. Back when he'd wanted to believe his father was a great man.
Here was Dumbledore, whom his father despised (and he had been taught to despise as well), looking at him with kindness even as a wand was threatening him, and offering to help him. Dumbledore, telling him that he still had a choice, and could be safe without killing anyone. Dumbledore, taking more care with Draco than Lucius had in years; understanding what Draco actually wanted.
Draco couldn't live a lie anymore.
As terrified as he was of dying, he knew he couldn't kill Dumbledore. He wouldn't be swept into that dark storm, and become something he wasn't.
His wand seemed to grow warmer in his hand (emanating from the unicorn hair core), as if encouraging him he was doing the right thing as he started to lower it, and he thought maybe - just maybe - this was what real bravery felt like.