She endured an abusive husband who likened her to "an infected tooth", and torture by Stalin's secret police, who stuck needles in her, threatened her children and drove her to the brink of madness. The tragic life of the wife of Sergei Prokofiev, one of the 20th century's greatest composers, is now revealed in hundreds of previously unpublished letters, as well as secret Soviet files.

The cruelty suffered by Lina Prokofiev at home paled against her later torture, but she never stopped loving her husband – even when he abandoned her for another woman – and she never spoke publicly of her suffering during eight years in a Siberian prison camp.

Prokofiev (1891-1953) is the composer of masterpieces such as the opera War and Peace, the ballet Romeo and Juliet and the children's fable, Peter and the Wolf. But when Simon Morrison, a British-born music professor at Princeton University and president of the Prokofiev Foundation, was given access to the unpublished documents by Prokofiev's family for a new book, he was shocked by their contents. They revealed "a real indictment of his personality", he told the Observer. "I have a moral question. Prokofiev's music is some of the most emotional of the 20th century, but he was a person of very little feeling. As a biographer, you have responsibilities. As a listener, I don't think I can listen to the music the same way again. It is a harrowing story." Letters from Lina to her children from the gulag are equally poignant, he added.

The 600 letters – whose contents are to be published on 21 March by Harvill Secker in The Love and Wars of Lina Prokofiev – were made available to Morrison by Prokofiev's older son, Svyatoslav, whose "dying wish was for his mother's story to be told in unvarnished guise".

Morrison said that Svyatoslav told him: "My mother always wanted to have her story told and she never herself could do it." Morrison added: "He gave me permission to look at intimate letters that had never been seen." They reveal a heartbreaking story of doomed love. In various passages, Prokofiev accused Lina of "bat grabbing" his hair and rarely displaying "acts of love". He criticised her for being manipulative, and wrote of his feelings for another woman: "It's only now that I recognise the barrenness of my life, excluding my work." With brutal bluntness, he told Lina that, when she kissed him, he felt like an adulterer, betraying his real love.

Until now, the correspondence was sealed in the Russian State Archive. Morrison said: "Nobody got to see it. It literally says 'categorically forbidden' because of its intimate nature. The family didn't want people going in there because they recognised that one could write a devastating indictment of the composer and what he put his family through. I sent my book to the grandson. He read it and he was deeply affected by it. He didn't interfere with it at all and said 'this is just devastating'. He himself had never gone through this material."

The Prokofievs were married in 1924. Several scores, including The Fiery Angel, were inspired by her. Seventeen years later, he left her for a woman 24 years his junior, and the marriage was officially annulled in 1948. During their marriage, they wrote extensively, as his touring kept them apart. But, despite his adultery, Lina never stopped loving him, pleading in her letters for reconciliation. In one letter she protested that she was neither "a freak nor an idiot", as he made her feel. Even when she knew of his affair, she wrote: "Well, go ahead and see her. I won't object; but that doesn't mean you have to live with her."

Lina was in her Moscow apartment one night in 1948 when the telephone rang and the caller insisted that she come downstairs to collect a parcel. In the courtyard, she was arrested. Charged with espionage and treason following her attempts, through the British and French embassies, to escape from the USSR, she endured nine months of interrogation and torture, spat on and bound in painful positions. Soviet files reveal the account she submitted to the prosecutor general in 1954: "For three and a half months … I wasn't allowed to sleep. I was driven to the point of madness … Having been made sick … the investigator 'consoled me': 'Don't worry, you'll be screaming even louder when you feel this truncheon down there!'…"

Once in a camp, her two sons were able to visit her and correspond with her. Her older son kept diaries. Morrison said that the correspondence and diaries provide a "first-hand account" of the horrors of a prison camp.

Even when incarcerated, her love remained undimmed. Until her death in 1989, she continued to champion Prokofiev's music and to give the outside world the impression that theirs had been an enduring love, despite everything.

Negotiations are under way for a possible feature film based on her story.