In Chapters 3-5 of Ethan Frome, what two sights does Ethan notice on his way home, and what is his response to each?

The incident you are refering to occurs in Chapter Four of this
great novel by Edith Wharton. Going home to his house, and looking forward to an evening spent
just with Mattie, as his wife is away, Ethan is contemplating his situation in life. He surprises
Ned Hale and Ruth Varnum kissing as he returns, and we are told that this brings bittersweet
feelings to Ethan, as this was the precise place where he and Mattie stood together longing for
each other:

It pleased
Ethan to have surprised a pair of lovers on the spot where he and Mattie had stood with such a
thirst for each other in their hearts; but he felt a pang at the thought that these two need not
hide their happiness.

Wharton thus
compares the two sets of lovers, and the way that Ethan and Mattie must conceal their love
because it is, by necessity, illicit due to Ethan's marriage. As he proceeds, he passes the
graveyard and sees the gravestone of his parents, who were together for fifty years. What saddens
him is the thought that he and Zeena might have exactly the same gravestone to commemorate their
'happy' marriage:

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Then, with a sudden dart of irony, he wondered if, when
their turn came, the same epitaph would be written over him and
Zeena.

Thus both sights that Ethan
sees serve to reinforce the impossible nature of his relationship with Mattie and his longing for
her, and all the obstacles that stand between him and happiness.