What is the significance of Montag's and Mildred's conversation before he leaves the house?

The significance in Montag and Mildred's discussion (Part II), is the fact that for all intents and purposes their relationship seems to be over. There's nothing left to say, and the evening ends with silence.

"Fool, Montag, fool, fool, oh God you silly fool..."

"Shut up!" He pulled the green bullet from his ear and jammed it into his pocket.

It sizzled faintly. ". . . fool . . . fool . . ."

He searched the house and found the books where Mildred had stacked them behind the refrigerator. Some were missing and he knew that she had started on her own slow process of dispersing the dynamite in her house, stick by stick. But he was not angry now, only exhausted and bewildered with himself. He carried the books into the backyard and hid them in the bushes near the alley fence. For tonight only, he thought, in case she decides to do any more burning.

He went back through the house. "Mildred?" He called at the door of the darkened bedroom. There was no sound."