To add to the previous post-
Chapter 9 is the pivotal chapter in which Mattie and Ethan make their suicide pact when Mattie told Ethan to "take her down again" (down the slope) so that they could sled down the school hill and hit the Elm tree hard enough to kill them both.
They did this because of the overwhelming fear of losing each other for good, and the prospects of life that were awaiting them- not good at all.
When Ethan agrees to the pact, he asks her to sit behind him. She continuously refuses and questions why he would sit in front. This is where the previous post makes a very good point about the reasons behind Ethan's choice.
However, Ethan's literal answer was: "Because-Because I want to feel you holding me."
From that, we can assume that he wants, in his last breath of life, to feel like a real man. Zeena, his wife, is a emasculating woman: She demoralizes, belittles, weakenes, and discourages Ethan in every way, shape, and form. Mattie is the opposite. She idealizes him.
Therefore, in addition to the previous post, we can also argue that Ethan is experiencing his very last wish: to be a protector to Mattie, to feel like a man in charge, and to do his first and last act of chivalry.