Sherlock is slowly becoming aware of things about John - like the fact that John works around Sherlock in the house, putting the coffee mugs safely on a high shelf, not complaining when Sherlock plays his violin at night, bringing home milk. He knows when John has a date, and how the date went. And when John lies on the sofa to listen to Sherlock play his violin, Sherlock covers him with a blanket.
When John goes to visit Harry for a few days, Sherlock becomes bored and angry and turns to cocaine. But by the time John returns, Sherlock is back to normal.
While on a case, Sherlock jumps into the Thames after a suspect. When John is upset over Sherlock's lack of concern for his own life, the two argue.
Excerpt:
"I can't change who I am, what I am, what the world makes me into." It's too miserable an offering, but it's all he's ever understood to have.
"And you're married to your work and that'll never change." Now they're both bitter, and Sherlock sees the end unfold, un-spiral, John walking out the door and all of this ending, and he's too proud to beg and not religious enough to pray, but he wants to.
"John, I--" He breathes in, slowly. "What I can offer you won't accept, and that's just our curse, I think."
"Sherlock--"
He cuts John off before his heart can be snapped in two. "I don't usually allow myself to be distracted by emotion. It shouldn't be a problem; you took me by surprise. I shall do my best in future, if you will stay, to not get in your way."
John frowns, pausing, and then he takes a step forward, and Sherlock only just manages to catch him when his leg gives way. Leaning on Sherlock, John stares, eyes wide, and then forces out, "I took you by surprise? What... Sherlock, what are we talking about?"
Burning Up Through Your Veins, by verasteine