Ted definitely understands the - well, not the lack of trust, exactly, but the need to personally do as much as he can. Ted experiences the same. He knows Sherlock is utterly devoted to Joan, and that he's probably better than Ted at looking out for her, at least when it comes to stuff that requires being observant or knowledgeable. It's pretty much Sherlock's main thing. But that doesn't stop Ted from worrying if he stays away from Joan for too long anyway.

He looks forward to a time where he doesn't have to worry about her. Not because it's an obvious strain on him (and on Sherlock), but because he does know that Joan can take care of herself. But right now there's some specific ways in which she can't.

As he waits for Sherlock to return, Ted finds himself ignoring his computer in favor of just watching Joan. Not out of worry, but out of fondness. He gently reaches out and just strokes her hair, as softly as he can to avoid waking her.