Okay so there's something about this scene. It could've happened anywhere at anytime but it happened in Baker Street. Not to mention Mary had literally told him to confess his love for Sherlock after he just told Sherlock to be with someone else. It's not okay because he again, feels like him and Sherlock can't be together. So he lets it out, standing in the middle of Baker Street he lets out seven years worth of tears in front of Sherlock the man he loves. Now about the hug, you can see Sherlock is debating whether to do something because after the last time he tried to comfort John he rejected him. But this time John is crying (there were no tears when Mary died) and Sherlock cannot watch John cry. He stands up and HUGS him. He could've put a hand on his shoulder like he attempted to do in TST and said "it's okay" but he didn't he held the back of johns neck and his arm and pulled himself and John close together. He did that. We've seen what a friendly hug looks like between the two and this isn't just a hug between friends. Sherlocks face when John said that he still wants more. I think Sherlock realised who John is in love with. This hug is so much more. John puts his head into sherlocks chest as Sherlock comforts him, and Sherlock rests his head against johns. And as it fades out you can see them trying to become closer than they already are, Sherlock pulls John in tighter and I think if it hadn't of faded out we could've seen Sherlock lowering his head next to johns. This isn't just a hug shared between two emotionally confused men it's a hug shared between two men who are in love with each other and have been for seven years. Not just an ordinary hug.