Previously unpublished letters are to shed light on the passionate relationship between Ernest Hemingway and an Italian teenager 30 years his junior.

Hemingway was married when he met Adriana Ivancich but said he felt as if “lightning had struck”, and a friendship developed between them over eight years.

A new book by the Italian author Andrea di Robilant, Autumn in Venice: Ernest Hemingway and His Last Muse, explores their friendship. Di Robilant makes public for the first time a dramatic letter in which Ivancich writes to him about her torment in having to cut off all ties.

In a letter dated April 1956, she told Hemingway that the man she hoped to marry “doesn’t want me to write to you any more and he doesn’t want you to write to me”. She underlined those words, adding: “[That has] made me suffer … and always will make me feel sad … I tried everything (you know how much I love you …). No tears, no words could make his mind change … I never thought that there could be a goodbye between you and me.”

There has been extensive speculation about whether Hemingway and Ivancich, who first met in 1948, were lovers. Di Robilant believes that, far from being a passing infatuation with a much younger woman, the friendship played a crucial role in regenerating Hemingway’s creative powers.

“She brought joy to his life, inspired him,” he writes, “leading to a remarkable literary flowering in the late season of his life.” Hemingway went on to write masterpieces such as The Old Man and the Sea, for which he won the Pulitzer prize.

In another previously unpublished letter, Hemingway wrote to Ivancich: “When I am away from you I do not give a damn, really, about anything … I miss you very much. Sometimes it is so bad that I cannot stand it.”