Remember that time when we all thought Mycroft was Moriarty. Remember that time when we all thought John was Moriarty. Remember that time when that gay guy turned out to be Moriarty. Well that sums up season 1 well
I think that Sherlock also wanted to prove to Seb that he could have a friend after all (because Seb knew him in Uni and they all hated him there). << yes! He was being like "this is my FRIEND. Yes I can make friends.
I'll admit that he thought Sherlock didn't do anything hadn't occured to me, but it had registered that he didn't know she saved Sherlock <<< that changes EVERYTHING! (okay maybe not everything, but a LOT)