"Liking the answer doesn't factor in. In our line of work it mustn't."

It's textbook, actually, albeit one written by Holmes. His denial is expressed as another compliment buried in a double negative, this promotion of her promise as an investigator by way of ridiculing and dismissing her current profession and professionalism.

She wasn't doing to deny it: his courtship of her as investigative partner, improbably championed by her own mother, was effective. The seeds inadvertently planted on day one were all but ready to be harvested. She had imagined staying on, becoming his associate, not having to let go, again. But it was her job, now, to model structure, promote healthy boundaries, teach limits and responsibility over impulse and desire. She had promised him closure and she would provide it, no matter what it cost her.

She knew the damage wrecked by broken promises.

She's simultaneously hurt (a warning sign, she knows, and this helps steady her resolve, and is grateful) and not at all surprised that he could imagine she wouldn't keep her promise: that she would be out of his life at the end of the six weeks, and that he'd be ready for it. Comparing the flinches and grimaces this topic had provoked just two weeks ago to his relative calmness tonight was evidence of her success. Their success. He was excelling at recovery. He just hadn't let himself deduce what the cost must be.