Even though I’m a Johnlock shipper, I like Mary’s character from the original stories. She was strong willed and a good match for John, and to be honest, she knew the importance of the relationship the two had. So, unlike John’s many ex’s, she would never put herself between them. Instead, she stands by John in love and loyalty, not trying to compete with Sherlock because she knows she doesn’t have to.
I love this scene. It sets up the entire episode. Sherlock is expecting to just waltz right back into John’s life with no hiccups. Everything will go back to just how it was with the snap of his fingers. What he doesn’t realize (not yet) is the severity of the consequences of everything that’s happened. The narcissism in him is convinced that John couldn’t possibly function without him by his side. It was true for both previous series’ as well. This sets up the greatest of gut punches when he realizes that yes, John did in fact move on. More than that, he’s living and loving in a way that he hadn’t before. And while there is a part of him missing since that day at Saint Bart’s, another part of him has grown. And Sherlock will have to come to terms with it if he is ever going to include John in his life again.