He can hear her, loud and clear. And he wish he couldn't, because each scream goes straight to his heart and it hurts so much to hear her. To know that he's the reason she's screaming and crying like that. And he wants to desperately turn around and try and fix things, but he's supposed to follow her wishes and not, right? That's what good friends do, listen to them and do what they want them to. But what if doing what they said to do cause more grief? He doesn't know which is better so he just keeps walking, rubbing his eyes and letting out soundless sobs.

He's just mouthing out 'I'm sorry' as he walks. She'll never hear it because he can't even hear it himself. The voice in his mind doesn't count.