The silence that settled into the lab was the sort that was comfortable, not awkward. Bred from familiarity and trust, there was a distinct lack of having to make the space more interesting, not requiring words to ensure the other's continued companionship. Neither Sherlock or Molly felt the need to fill it with inane babble or social niceties; Molly: because she knew that Sherlock wouldn't even appreciate it, Sherlock: because it was pointless and would be insincere.
Insincerity was something that he had specifically dropped out of his dealings with Molly Hooper.
It was the least he could do after what she had done for him.
Prior to his fake suicide, Molly Hooper had existed on the periphery of his life, a somewhat quiet presence in the lab, a helpful hand in the morgue, and a means to access both. She'd been someone that he could get the superficial satisfaction of knowing he was attractive (in the rare moments he felt the need to prove such) and a less whiny method of gaining sustenance (John being apt to complain before finally going to get coffee or food).
Then she had seen him. Really seen him. He'd thought himself above sentiment, in control of his emotions. With a quiet word, a simple, albeit stumbling, observation, Molly had cut to the heart of the matter. And in that moment, he realized how much she counted. He may not have known then what she could do for him, but he'd known that he could rely on her and she would not break, would not run, but stand strong.