Cade has gone from fight mode to flight, and Nerva holding onto him is wracking up his nerves. "I'm sorry," he whimpers, unable to form a further explanation because he doesn't even know where to start. On some level he understands he's in the wrong, and therefore saying anything beyond an apology would be a waste of everyone's time.
"...I don't know, I'm sorry," he continues desperately, and he tugs again at Nerva's grip. He hasn't been held onto like this in recent memory, and it's unsettling. He has to get out of here, he's ruined everything. He resolves, in his panic, to leave the camp, to go where no one can find him or will ever have to see or talk to him again. He just... needs Nerva to let go first.