Imagine for a moment the reason Sherlock told Mike Stamford that he was looking for a roommate at the beginning of ASiP. Sherlock had already moved in to 221b and certainly didn’t need help paying the rent. We know what kind of man Mike is from context clues in the show as well as on the blog. He doesn’t have many friends, he teaches now, and Sherlock calls him out on the blog for trying to “act cool” when he clearly isn’t. Mike recognized John immediately when seeing him in ASiP. Mike knows about Harry and John scoffs at him when he says she could help. This shows Mike may even know a bit about the family dynamic. Mike even knew John had left and gone to war. That’s a lot of information for Mike to know if John were just some random classmate of his. Either they were pretty decent friends (“That’s not the John Watson i know”) or Mike likes to gossip about old acquaintances and relive the glory days (“Bright young things like we used to be, God i hate them”). I favor the latter. Either way, I’m certain in the years Sherlock has known him before ASiP, Mike has rambled on and on about the great friends he had in uni and the ridiculous adventures they went on. Sherlock would mostly tune that boring stuff out, but would listen intently to the way Mike described all his fun, smart doctor friends. He may have even heard about that one “ladies man” who was bored with being a doctor and went to war instead. I bet Sherlock told Stamford that he was looking for a flatmate just to see who he’d bring around, since Mike knows so many doctors and interesting men. I think this was his way of setting himself up with men. Sherlock would know right away if there were any chance at a relationship/friendship within the first 2 seconds of meeting a person so the false pretense of looking for a flatmate would work perfectly. Since cases are like dates to Sherlock, bringing John out on one immediately and having him say “I’m supposed to be helping you pay the rent” and “This is more fun” shows the “flatmate” part wasn’t important at all to Sherlock. Probably never was. He just wanted to see which of Mike’s cool friends he’d introduce him to. And what luck! He finally met that hot army doctor after hearing about him all these years.
