John sometimes compares Sherlock to an exploding star. He is grand and exciting, unpredictable and beautiful (John isn't gay, but he isn't stupid either). He thinks that maybe Sherlock knows that this is how he views him. He doesn't miss the tiny smirks when John is yet again flabbergasted at another correct deduction (although really he should be used to it by now), he doesn't miss the looks when he tells Sherlock to slow down, he doesn't miss the small snorts and the barely suppressed laughter, and John thinks, rather embarrassingly, that Sherlock knows that he stares at him.
It's not like he can help it. Sherlock is almost heavenly, other-worldly and dazzling, just like a rupturing star. He is breath-taking just to look at, but when he talks, my God does John feel stupidly overwhelmed. He talks so fast that John wonders how he keeps up, thinks Sherlock is purposely making him feel like this for some sort of crude experiment.
No matter what the Doctor does, the Detective is always a step ahead. It's good though, because then they balance each other out; Sherlock brings out the best in John, making him run faster, think faster, providing him with adventure and the thrill of the chase, and John brings out the side of the dark haired man that not many other people see, the domestic, lazy, homely side of the reckless man that everyone knows but doesn't always love.
The older man didn't know how people could shun Sherlock, didn't understand why they called him a freak and looked at him disgustedly. Until he realised that they were just jealous. The detective was everything they were not. They had all become police officers and detectives to be the best, to capture the most criminals and immortalise themselves in police history, but unfortunately they had never bet on Sherlock Holmes.
John sometimes can't quite believe he is real. He is so fast it's blurry when he moves, so quick minded and sharp tongued and sarcastically witty that it is wondrous that he even exists. He is like so many supernovas and beauteous explosions of the stars, so many years away but so close at the same time; he is both old and wise beyond his years, but young and naive of a normal human life.
John knows that also, while he is all those things and that he is constantly in awe of him, he is worried too, because although he is impossible and wonderful, he is also troublesome and destructive, both to himself and others. He waits for the day that Sherlock does himself or someone close to them harm. He is a potential danger to everyone and yet John stays, whether out of excitement or out of loyalty and love (he knows he loves Sherlock, that much he is sure of) he doesn't know, but he stays, close, always. He is always worried, always on edge, always jumpy, but he has to be with him because no one else will and he has a duty as Sherlock's friend to look after him and be there for him throughout the chase and the capture. The Doctor is always wary, because after all, sometimes exploding stars turn into black holes.