John often finds himself wondering just why he follows Sherlock the way he does.
Yes, Sherlock makes him feel alive. Yes, Sherlock lives dangerously and yes – OhgodYES! – it makes him feel so real... but that's not Sherlock himself, is it? It's his lifestyle, the way he lives, not just the fact that he's alive.
John tells himself that's what it is - that the racing heartbeat, adrenalin and fierce anticipation all come from the way that Sherlock and – by default now – John live. Of course it does - the running, the mysteries, the running, the borderline illegal activity, the running, the life-threatening situations and the running - all perfectly reasonable causes for the accelerated heart-rate, irregular sleeping patterns and inability to maintain any kind of long-term romantic relationship.
John can usually believe this. Usually.
He tries not to think that the only reason he can usually believe this is because he and Sherlock are usually running or engaging in borderline illegal activity or getting almost-shot or running. Usually.
John Absolutely-Does-Not-Think about how he feels when he and Sherlock just sit. Well, John sits, Sherlock tends to bounce. Even when he's perfectly still, Sherlock bounces.
John Absolutely-Never-Ever-Does-Not-Think (and-how-could-you-suggest-such-a-thing?) about all the times that Sherlock's bouncing-but-not-bouncing makes him laugh. Nor does he think about all the times that Sherlock's thinking at the window - staring off into numbers, words and pictures that only Sherlock can see- makes him smile.
And he really doesn't think about all the times that Sherlock's refusal to eat, his inability to sleep and his total lack of power to understand absolutely breaks John's heart.