[He looks down at his plate a few moments, unsure of what to say. He could say he's undeserving, which is how he feels, but he knows she would disagree with him, and come up with kind things to say.
He decided that, if anything, the least he could do is show appreciation for her going through the trouble of dealing with him.]
You don't have to do that. Thanks, though. Your kindness is always appreciated.