In "The End of Something", what words or actions of Nick and Marjorie indicate that the relationship between them is strained?

The two eat without talking.... something that seems to be out of the ordinary.

They ate without talking, and watched the two rods and the fire-light in the water.

Marjorie knows that something isn't right and asks Nick what's wrong.

"What's the matter, Nick?" Marjorie asked.

"I don't know," Nick said, getting wood for a fire.

"You don't have to talk silly," Marjorie said. "What's really the matter?"

Nick is short with Marjorie, inferring that she believes herself to be a know-it-all.

"You know everything," Nick said.

"I can't help it," Nick said. "You do. You know everything. That's the trouble. You know you do."

"I've taught you everything. You know you do. What don't you know, anyway?"