Even though I'm the sacrifice,
You won't try for me, not now.
Though I'd die to know you love me,
I'm all alone.
Isn't someone missing me?
"Missing" by Evanescence,
Part 2: [link]
I imagine that it was a rough 3 years for Sherlock, he comes back and John is all pissed off at him so he relapses.
I have an inexplicable love for stoner Sherlock.