"I had reached a point at which the future stretched long and dull ahead of me. I was, remember, a young man, scarcely thirty, and the thought of returning to the choking fogs and humdrum life of London was suddenly intolerable."

Jeez, I feel like that almost every day! And I don't have nearly as much pressure on me as Holmes did then. The man sounds like he was one step away from either a complete nervous breakdown, or suicide. I felt pity and sympathy when I read the whole scene. Yes, it was rather cruel to leave Watson like that, but not unforgivably so. And certainly not intentioanlly so, at least not in my opinion.