The physical tells as he tenses are subtle, but he knows himself well enough to guess they won't be missed. A slight tension in his jaw, the way he flexes his left fingers as if wishing he had a wand. They're small and subtle, but there.

"I don't intend to leave her again. But if I should, Narcissa is perfectly capable of caring for herself, though I thank you for your concern." A slight beat. "I trust you're done assaulting her, then?"

This could be going much better.