Leaving himself open meant leaving room for an attack. Mycroft always taught him that caring was not an advantage. Not that he hadn’t learned it from experience rather early in his life.
He carefully suppressed his feelings, desires and dreams for years. It had become easier with time, now it was almost second nature. Or so he had thought. But somehow people started to feel closer, he somehow opened up more than he should have. John, Lestrade, Mrs. Hudson.
He became vulnerable. It was unacceptable. This business with Moriarty was the proof of that.
Starting again from scratch was an option, but he got a taste of something he had denied himself for so long and he wasn’t ready to give it up yet. Not good.