in chapter 5 what does ethan mention that dampers the mood

The conversation becomes awkward; Ethan brings up Ned and Ruth in hopes that talk of the young couple will somehow open up a chance for a soft touch. It doesn't work; the conversation turns to Mattie leaving someday, and Mattie worries that Zeena is displeased with her. She worries that Zeena will force her to leave. Ethan expresses his dismay at the idea of Mattie's departure, and his earnestness makes Mattie blush.