A thought - merely a thought - suppose Sherlock is playing “I’ll reject you before you reject me” when he embarrasses Molly (and himself) in this scene? He assumes she has another love interest - that he is no longer the object of her affection. In his mind, he now has a rival… Shades of brothers rivaling for Mummy’s attention and affection subconsciously dictate his course of action… Must not feel pain! Must push away Object of Affection before said Object can inflict wounds! Too late, too late, that gift, that dress… Evasive maneuvers! Quick, man, for your life, lest this heart-of-stone begin to beat again (why does my heart hurt? You’ve never used it before - not since…) But then - a eucatastrophy. Her cap is set at no other, her affections safe. She has always counted, and he can always trust her. Maybe this scene set the “always” in its perfect place. He hardly knows what to think, say, or do. And she, once again, through clouds of her own insecurities, experiences the kindness of this man. He is a good man, after all, for only a good man can admit and amend his wrongs. Ah. She was right to set her affections on him. There’s the gold in the heart of stone. He is worth the risk.