Strait is the Gate( La Porte Étroite)
by André Gide
Sometimes when you read Wikipedia pages they are amazingly concise with no extra details. For example, the Wikipedia entry for this book has this to say:
The story is set in a French north coast town. Jerome and Alissa as 10-11 year olds make an implicit commitment of undying affection for each other. However, in reaction to her mother's infidelities and from an intense religious impression, Alissa develops a rejection of human love. Nevertheless, she is happy to enjoy Jerome's intellectual discussions and keeps him hanging on to her affection. Jerome thereby fails to recognise the real love of Alissa's sister Juliette who ends up making a fairly unsatisfactory marriage with someone else. Jerome believes he has a commitment of marriage from Alissa, but she gradually withdraws into greater religious intensity, rejects Jerome and refuses to see him. Eventually she dies from an unknown malady which is almost self-imposed. (WIKIPEDIA)
AND THERE YOU HAVE IT FOLKS. André Gide won the Nobel Prize for literature in 1947- he got four titles into the 1001 Books list- The Immoralist, The Counterfeiters and Fruits of the Earth. Gide had a lengthy, prolific career- so much so that his author page on said Wikipedia is called a "partial" list of works- and even that has something like 50 titles listed- some novels, some non fiction.
My best take on Strait is the Gate is that it represents an intermediate step between the 19th century bildungsroman and the 20th century existentialist love story, with strong elements that point in both directions. The Penguin Classics edition is only 128 pages- making Stait is the Gate something close to a novella.