These sequences were kind of symbolic of what Sherlock and Joan have, right? Throughout the episode (even in the previous one) Lestrade encourages Joan to leave Sherlock and find a job for herself because she deserves better. Because he screwed up and now he thinks ‘it won’t last long’ for Joan either. But does Lestrade really know Sherlock? No.
Joan has faith in Sherlock. Sherlock might screw up sometimes, but Joan knows Sherlock and she has decided to stay…