Sherlock is so cruel to Watson...
because he has such poor people skills, he doesn't really know how to be a good friend.
Watson is loyal to a fault; who is this Mary?
I actually thought Mycroft set Watson up under the Guy Fawkes bonfire to get him back into Sherlock's life, until the end scene.
Shows you what I think of Mycroft, huh? He's not much better at this "friend" stuff either.