Defeat did not sit well with Galad, and he'd always known that about himself. What surprised him was the way he felt when Mr. Cavanaugh told him he was disappointed in him. Galad had never lived to impress others. He barely lived up to the expectations of his parents. No one else was important to him. Not even, he would wager, his betrothed, Felicity.
Mr. Cavanaugh being disappointed in him felt like a slap to the face. Here was the only authority figure Galad had even remotely respected - through hours of detention interviews - and he was disappointed? Rather than feeling the sting of the words, Galad felt fresh betrayal. The one person he had confided in had so easily lost faith in him, did not understand him. What was even the point, then? Mr. Cavanaugh might as well have literally planted his flag on Gilderoi's side of the battle.
Galad felt his heart harden, protecting itself, and he left the banshee's office in his usual style: loudly with a slamming of the door.