I love how Downey discusses Holmes and Watson's relationship. First he jokes about their "circumstantial homosexuality," then he says:
We kept talking about getting into the spirit of 'What does it mean when two people are so close they almost can't stand each other, but they can't stand on their own without each other?'
It means love of course. Whether you believe it is merely platonic friendship or passionate romance, it is certainly a deep and lasting love.
I'm so glad that Downey and the filmmakers perceive that Watson is not always idolizing Holmes blindly and following him around like an obedient dog. Watson is more complex than that. Holmes is frequently annoying, depressingly cynical, and emotionally abusive in the canon. It's only normal and natural that Watson might not be able to stand him sometimes. That must be why he mentions having other friends besides Holmes, such as Thurston, and why he occasionally jabs back at Holmes, like with his "pawky humour" in VALL.
There is a tension between them, an ebb and flow in their relationship. Often they separate, like when Holmes solves cases on the Continent alone, or like the strangely empty year of 1890 when he and Watson drifted apart again. There's no need (for Brad Keefauver, for example) to invent extra wives for Watson to explain his absences from Baker Street. He may simply need a vacation from Holmes sometimes and may want to establish his own career so he can feel more independent.
Of course as always, he returns because Holmes is an irresistible draw, even when he's a total bastard faking his death for three years. They truly cannot live without each other in their lives. It's always struck me as odd that ACD wrote them drifting apart again once Holmes retired. Let's hope that Watson's service in WWI still allowed him to stay close to Holmes after LAST.