Dr. John Watson shot a man for your brother when he barely knew Sherlock. He refused money without knowing how much, and he helps Sherlock even when it inconveniences him. It inconveniences him a great deal, you know.
Dr. John Watson killed a man for Sherlock. He risked his own life to protect Sherlock. You understand the appeal of Sherlock, of course. There is a very short list of things you wouldn’t do for your brother, and that is only because they are impossible according to current laws of existence. (You’re working on that.)
But Dr. John Watson is ordinary. Physically, he is ordinary; mentally, slightly above average; and though he is very loyal, he’s also unforgiving.
According to everything you know, he should have left Sherlock sometime in the first week—instead, he followed Sherlock to a murderer and shot the man dead. And he stayed through two kidnappings and a bomb on his person and a million small slights and annoyances and the violin for days at a time.
You know your brother better than anyone. You love him above all else. And still, you could not cohabitate with him.
But Dr. John Watson can, and Dr. John Watson does, and you hope Sherlock never commits an act that Watson finds unforgivable. If you have to vanish the man for breaking your brother’s heart, Sherlock will be most annoyed.