She's chipping away at him, slowly, in undeniable ways. He doesn't have to allow it, he could stop her and simply refuse to answer. He's still operating under the assumption that withholding the most intimate of details wouldn't cause her to suddenly stand in judgment of him, yet it would inhibit a greater intimacy between them. He's so rarely breached this line with anyone and part of him remains ever curious, ever more alarmed at the power she holds with her mere words and touch. He's not entirely sure how it happened and it's caught him off guard. Was he so desperate to be known that he's now latched on? What does he owe her?

Part of his willingness to answer, admittedly, is an almost scientific inquiry as well. How far will this go? What awaits them at the end of it? If he gives her what she asks of him, what might he gain in return? He can't begin to guess and he's unsure what he would hope to receive.

"No one should ever die for me," the Doctor's voice is firm, leaving no room for doubt in this.

But her second question gives him pause. He's not alarmed by it, given that he's asked equally intrusive questions of others in his time. It takes consideration to answer, not because it troubles him, but he's genuinely curious why she might like to know. Perhaps the why will reveal itself when he answers.

Covering her hand, he answers her with a truth that has a twist to it. Not a direct answer, but an answer all the same, and one that allows him more control over the way he wields his words and his perspective on what happened.

"This moment between us, it's a good one, I think, as moments go. Certainly, could do with a few improvements but...I'm glad to be here for it."

He's glad he didn't die and he's sad that someone else did. Like so many things with the Doctor, the two truths live together quite well in his head.