You John. You.
I think the best part of this scene is that John realizes as he says it that it’s him. He’s just sat down in his chair; he thinks: my chair is back. Why is my chair back? Oh. It’s me, isn’t it. Sherlock is protecting me.
That chair means that Sherlock thinks that John’s coming home. Or he ought to be. That must have been John’s first inkling that it was Mary who shot Sherlock. Slowly, slowly, John learns to speak Holmes.