"Lean on me when you're not strong and I'll help you carry on 'cause soon I'm going to need somebody to lean on." Sorry had to, this is really sweet, Sherlock looks so tired and weak.
I love how you've portrayed Sherlock's fragile state here. Not quite sure if that's what you were going for, but that's how it spoke out to me. That slight smile, slight frown, on John's face, too, makes me wonder what the character is thinking. Very nicely done - well done!!
But seriously, this is sweet.