Nathaniel isn't entirely surprised. There is hurt, yes, but from a blow he partly expected would come anyway. He's never been enough for anyone, and Anders has a history.

"All right," he says calmly, then suddenly stands up, pulling out of Anders' grasp. "All right." He starts pacing the tent. "Yes. Yes, you had to tell me. It's not like I could have foreseen that you'd move on to something else once things are too good. That's not in your history at all."