If you want to make John Watson fall for you, you’ll have to do your best to look like Sherlock. We talked a lot about all the similarities between Sherlock and Jeanette in ASIB: the hair, the the height, the long dar coat, the manners, etc.
I remember that someone said the same thing about how Mary is introduced (if some of you can link me the post I’ll add it) in TEH. She has a lot of Sherlock’s attribute on her: the dark wool hat to mimic Sherlock’s dark hair, the blue scarf, the coat, and she also looks a bit taller than John. She tries so hard to be like Sherlock, but as we can see the results are a poor copy.
Why she does this? Because she needs to attract John and secures him in her life in a permanent manner. Because he is her asset, her assignment. In the restaurant scene Sherlock himself shows up to interrupt the proposal. This way, Sherlock attempted to prevent that John joins his life with a fake Sherlock. He partially succeeded, because the proposal to Mary is never made (and the only proposal we see is from John to Sherlock), but the wedding occurs anyway.
But Mary is not the only mirror for Sherlock in THE. The man that drugged John in the very door of Baker Street is very Sherlock-y: tall, long dark coat, black hat, black leather gloves. He makes John fall for him while he is looking longingly to the door of the home they shared, while he is thinking in all of those memories together.
The fake Sherlock uses a symbolic phallic object to take him down, for me this symbolizes the sexual desire that John has for Sherlock. We got a very clear shot of this
Look at this cozy shot of John hugging the fake Sherlock, he is holding to him for dear life. And Sherlock looks at him with a really tender look, to be a kidnapper.
This fake Sherlock exposes John’s desire and Sherlock’s feelings. Sherlock saves John, because in a symbolic level he can’t allow John to burn and consummate his sexual desire with a copy of himself. He is the real, and that sexual urges will only be consummate with him. The same way he tried to interrupt the proposal, because he couldn’t allow John marry with another copy of him, because he is John’s other half, the love of his life.