Joan listens, the meaning of his words absolutely clear.

"That must be hard," she says softly. "Being afraid of being seen. It shouldn't be that way, but I know it is. I think it's important to remember that nobody owes anyone details of their personal life. I'd never reveal that sort of information about anyone, and especially about people I love. And clearly Sherlock wouldn't either."

Sherlock didn't even tell Joan, after all.