The first sign is always the shopping bags.
Some days when John arrives back at 221B, he will then see the dozens of bags strewn across the floor.
There's always a reason - gifts for Sherlock's homeless network, jumpers John might want, bonuses to be tossed in with the rent for Mrs. Hudson, random items that may have a use some day.
It's not like he can't afford them, Sherlock tells John, his words rushing out as fast as he can think of them. He does have the money to spend. Why not spend it?
John stays quiet. He finds himself taken to the best restaurants in London, and if they can't get in due to lack of reservations then Sherlock just takes him elsewhere.
There is a full meal each time - try this John, don't forget a dessert, let's have a bottle or two of wine. If things are especially bad Sherlock will start treating the people around them to free food and drink. Sometimes this brings smiles, but much of the time the diners are wary of this man who cannot stop talking, gesturing, and orders a full meal but eats only a few bites before going on to something else.
And yet, John feels a certain desire for these times. Perhaps it is because when they end, Sherlock is dead inside, and his talk of boredom with life takes on a darker tone than the usual.
At least during the high periods, he gains some measure of happiness.
The sunshine is mocking him.
Sherlock can't stand the fact that it is a perfect day outside, that even the weather seems to be saying the words no good, worthless, freak over and over again.
John will come to his door and knock, asking him if he would like something to eat. Sherlock can't imagine eating anything - his appetite is completely gone, and even if he does manage to eat all he then can think of is all of the people in the world who deserve to have what he has. He tells John to give it to someone who is worthy of eating. John just says "Fine," and doesn't push the issue. No tears, no fuss.
(the only time John cried in front of him was when Sherlock explained why his bedroom door was always locked)
If he does end up making it out of bed, Sherlock then will often wind up on the couch. Sometimes John will call Sarah with an excuse to stay home with him (and now you're making his patients suffer, how much more despicable could you get).
He makes no demands of John during the bad times. When he has returned to a more even state, Sherlock pushes and pushes John away from him. He knows that John will hate him one day, just like everyone else, and this way he has some power over when it happens.
Because, how could someone so caring love someone so worthless?
John, to this day, doesn't know what made him ask the question.
It ended up coming out one morning. It had been a good few days for Sherlock - while it had still been some time since the last case, John had yet to see any shopping bags or the sight of Sherlock lying on the couch with an expression of utter misery. Dealing with a pot of eyeballs on the stove was a small price to pay.
The exact reason he asked might have been lost, but his words were not. "It's a fire hazard, you know."
Sherlock had glanced at him. "I'm sorry? I can assure you I know how to be cautious with my experiments."
John shook his head. "Not that. I was talking about the fact you always have the door to your room locked whenever you're inside. If you were to have something happen, that could be dangerous. I will say right now that if you have the door closed, I won't come in."
The detective had then turned to look at the wall. "I trust you. It just happens to be a habit I fell into during university. Sebastian used to come into my room at night around two or three nights a week."
John could hazard a guess as to what had happened then. Sebastian, when he had met the man, had struck him as a bit of a bully, and he could see the man finding it hilarious to play pranks on the "freak" in order to build himself up. "So, what was it he used to do?"
"Oh, sometimes he would just rub his hands on me, or he would have me suck his cock, or he would fuck me. I never knew what it would be, and given my overall dislike for sex it wasn't all that fun. I now choose to keep other's access on my terms."
The neurons of John's brain were misfiring. All he could think was does not compute! "Didn't you ever say anything to anyone about what happened?"
Sherlock look genuinely surprised. "No. I always have felt that one's sex life is their own business unless it relates to a case of some sort."
John felt as if he had just entered some kind of modern horror film. "I meant that he was assaulting you. Why didn't you inform someone at uni?"
"Assaulting me? Oh, no. I never told Sebastian the word no or that he should stop. It wasn't assault - he had no reason to suspect that I didn't enjoy myself, or that I didn't want it. The fact that it was uncomfortable was due to the fact that I have always hated sex - John, is something the matter? Why are you crying? Have I upset you?"