Martin freezes when Jon snaps at him, staring at him in something like surprised terror, before he shatters and leans over, weeping openly against his own good hand. It's just too much, the thought that this was his fault, no matter what Jon insisted - the stupid, ugly wish that he'd been killed too, if only so he didn't have to deal with this.

He just needs a moment. Not long, but long enough to calm himself down.