221B has ~two~ occupants. As it should.
In a surprise twist, it's not Wilson who's been unfaithful to Julie but quite the opposite. The impression given is that the straw has finally broken the camel's back and Julie has asked him to leave. (I'll have to review that and the transcript isn't up yet.)
Wilson turns up at House's apartment front door and, in a moment of weakness (heh), House offers him shelter....of course, it's couched in the phrase, "Wanna beer?"
In the Canon, Dr. Watson first takes up residence in the rooms at 221B in 1881. In December of 1887, the mysterious first wife dies. In 1888, Watson married Mary Morstan and, presumably, moved out of 221B. In 1891, Mary Morstan dies. By 1894, Watson is back at 221B and this is probably the closest parallel....sadness in marriage led Watson to return to Holmes and the inimitable Mrs. Hudson.
By 1902, however, Dr. Watson had remarried and moved to Queens Arms Street where, as far as we know, he remained until his death in 1929.
Information taken from the Canon and from: http://webpages.charter.net/lklinger/Chrotabl.htm