Why these tropes fit

A frame narrative in which a nameless engineer visiting wintry Starkfield, Massachusetts becomes fascinated with the crippled Ethan Frome. Twenty-four years earlier, lonely farmer Ethan, trapped in a joyless marriage to the hypochondriac Zeena, falls in love with her orphaned cousin Mattie Silver, who has come to help with the housework. Jealousy flares when Mattie dances with local Denis Eady, and Zeena's suspicion grows after a lost house key. During a brief night alone together, Ethan and Mattie share a romantic dinner before Zeena's return ends the interlude, her discovery of a broken wedding-gift pickle dish sealing Mattie's banishment. Unable to fund a planned elopement and overwhelmed by guilt and hopelessness, the two lovers instead steer their sled into the deadly elm tree. They survive but are left broken, and in the present-day frame, the engineer discovers Mattie, now spinal-paralyzed, living on as a bitter dependent in Ethan's household alongside Zeena.

Read the source evidence

Tragic Romance: “Mattie suggests that they sled into the elm tree and kill themselves. Ethan agrees and they smash into the tree.” source
Forbidden Love: “Ethan has fallen in love with Mattie” source
Love Triangle: “He peeks in the windows of the church basement and sees Mattie dancing with Denis Eady and is jealous.” source
Small Town Romance: “It's winter. A nameless engineer is in Starkfield, Massachusetts on business and he first sees Ethan Frome at the post office.” source
Angst: “They all three live together, an unhappy family in the Frome house.” source

Metadata source: Open Library. Quotes are used only to verify the tags.