| Quote #1
His wife had never shown any jealousy of Mattie, but of late she had grumbled increasingly over the house-work and found oblique ways of attracting attention to the girl's inefficiency. (1.13)
Ethan is blind to Zeena's perspective. He seems to think that unless he and Mattie speak or show their love, they are not betraying or deceiving Zeena. He notices that the increase in their passion results in an increase in Zeena displeasure, but he can't do the math.
| Quote #2
Zeena herself, from an oppressive reality, had faded into an insubstantial shade. All his life was lived in the sight and sound of Mattie Silver, and he could no longer conceive of its being otherwise. (1.32)
Now we understand why Ethan can't figure Zeena out. He's stopped even seeing her as a person. He grew to hate her because she oppressed him, and in the process forgot that she sees and breathes and feels. As such, he fails to see that his behavior is at odds with his moral code. He hates lies, deceit, and hurting people, but he is definitely hurting Zeena by not being honest.
| Quote #3
Her nearest relations had been induced to place their savings in her father's hands, and though, after his death, they ungrudgingly acquitted themselves of the Christian duty of returning good for evil by giving his daughter all the advice at their disposal, they could hardly be expected to supplement it by material aid. (3.5)
At least from Ethan's point of view Mattie's relatives (including Zeena) are a rough crowd. They send Mattie to Zeena on the pretense of helping her, but with an eye toward punishing her for her father's mistakes. The "advice" mentioned was probably nasty and barbed, like the advice we hear Zeena give her.