Sherlock: you work with detective Lestrade and while on a case You and Sherlock meet and instantly hit it off. You end up seeing him on most of the cases he works on and finally he asks you out.
John: John was an old friend of yours and you had run into him having a row with the Chip and pin machine. You guys exchanged numbers and went out for coffee. You don't mind his roommate Sherlock and you two are now friends.
