I just realised a thing.

In s1e2 we had Sherlock calling John his friend, only for John to deny that with being a ‘colleague’.

We didn’t hear about that until s2e2, where Sherlock calls John his only friend, but only after John himself said he was Sherlock’s friend the night before.

Now, when Sherlock comes back in TEH, I think after what he’s done to John and learnt the repercussions of it, he probably isn’t so sure of if John would consider him a friend anymore.
So then we have Sherlock in s3e2, being chocked by John calling him his best friend. He then reciprocates and starts calling John his best friend often after this.

… I’m kind of seeing a pattern, with this occurring in episode 2 in every series, which is always the kind of ‘middle-ground’ episode, in that big things often happen in the first and last episodes. Could there be more of these friendship revelations to be had in the next s4e2? I don’t know, I don’t think there’s much more to add than best friend in the platonic department.

Maybe it’s just a coincidence. Or maybe there are more revelations to be had. I like patterns.