Let us remind ourselves that similes and metaphors are both examples of figurative language when one thing is compared to something else that is normally not associated with the first object. The comparison helps us see how the two objects can be compared. A simile is a comparison that uses the words "like" or "as." A metaphor is when the comparison is asserted directly, without these two words.
Examining this chapter, therefore, Ethan Frome himself uses a simile to describe how dark it is outside, saying "it's as dark as Egypt outside." A simile is then used to describe Mattie's face:
He kept his eyes fixed on her, marvelling at the way her face changed with each turn of their talk, like a wheat-field under a summer breeze.
This is a highly appropriate agricultural comparison for Ethan, as a farmer, but it also reflects the way in which Mattie's face is so changeable and attractive as she listens to Ethan's words, or his "magic" as he describes it. There are two similes to get you started. Now you need to go back through Chapter Five and see if you can identify any more. Good luck!