In April 1970, Robert Lowell met the writer Caroline Blackwood at a party in London. Lowell, at 53, was one of the most celebrated American poets of the era. Although he had a wife and daughter back in the United States, he and Blackwood hit it off; by her later account, he moved into her house that very night. On June 20 he sent his wife, the novelist and critic Elizabeth Hardwick, a telegram alerting her to trouble: “Personal difficulties make trip to New York impossible right away.”

It seems that Hardwick knew immediately what kind of “personal difficulties” were likely involved. The two had been married for 21 years, and during that time Lowell had suffered from periodic bouts of mania, during which he frequently fell in love with other women. These infatuations would dissolve once Lowell was well again. But Lowell’s illness had been stabilized by lithium treatments, and this was no mere episode — the feelings were serious. England was his new home, Blackwood his new partner; his marriage to Hardwick was essentially over. By the end of 1970 Blackwood was pregnant; he would marry her in 1972, shortly after he and Hardwick were divorced.

The Dolphin Letters” collects letters from this period, mostly by Lowell and Hardwick themselves but also by their daughter, Harriet, and by friends including Elizabeth Bishop, Mary McCarthy, Frank Bidart and others. Edited by Saskia Hamilton, the book begins around the time Lowell met Blackwood and left Hardwick, and continues until shortly after his death in 1977. The events and emotions it documents will be familiar to those who have endured a painful divorce: the angry recriminations, the sad or resentful outbursts, the second thoughts, the eventual grudging acceptance. (It is no accident that the first work of fiction Hardwick published following the divorce was titled “Sleepless Nights.”)

But the Lowell-Hardwick split was in certain ways worse than many. As writers, Lowell and Hardwick were to some degree public figures; their pain was destined not to remain private. And Lowell exacerbated the degree of exposure, and the pain that attached to it, by incorporating their ordeals and his adventures into his poetry.

Since the publication of his most famous book, “Life Studies,” in 1959, Lowell had been regarded as one of the founders and central figures of the “Confessional” movement in American poetry. Now, though, his poetic confessions seemed almost designed to cause hurt and invite rage. The year after marrying Blackwood he published three books: “History,” “For Lizzie and Harriet” and “The Dolphin.” The first two largely represented material from earlier publications; but the new poems that made up “The Dolphin” offered a frank and intimate account both of Lowell’s split with Hardwick and of the new love and the renewed happiness he had found with Blackwood. Moreover, Lowell incorporated passages from Hardwick’s letters into the book, rewriting and rearranging them, thus inviting the accusation that he had publicly misrepresented the woman whom he had already, albeit somewhat more privately, betrayed and wounded.

After “The Dolphin” was published, Hardwick wrote to Elizabeth Bishop that the book had “hurt me as much as anything in my life.” In an angry letter to Robert Giroux, Lowell’s American publisher, she complained that “I know of no other instance in literature where a person is exploited in a supposedly creative act, under his own name, in his own lifetime.” Lowell had been warned by several friends, including Bishop, that the book was irresponsible and would damage Hardwick. Though he had revised it in an attempt to soften the blow, he was unable to hold it back. To Bishop he explained that he “couldn’t bear to have my book (my life) wait inside me like a dead child.”

Lowell once said that the plot of “The Dolphin” was, in essence, “one man, two women.” But much of the interest and drama of “The Dolphin Letters” are generated by the deep divisions within Lowell himself.

Describing the dramatic personality changes caused by his illness, Hardwick wrote, “His fate was like a strange, almost mythical two-engined machine, one running to doom and the other to salvation.” Lowell wrote to Hardwick in October 1970, “I feel like a man walking on two ever more widely splitting roads at once, as if I were pulled apart and thinning into mist, or rather being torn apart and still preferring that state to making a decision.” Later in the same letter he told Hardwick that he couldn’t go back to her.

He was never entirely done with Hardwick, though. After the grief and rage subsided, the two managed to forge an amicable long-distance relationship. In the last year of his life, he returned to the United States while his marriage to Blackwood was foundering. In the spring of 1977 he moved in with Hardwick. “There is no great renewed romance,” she wrote to Mary McCarthy, “but a kind of friendship, and listening to his grief. . . . It could be said we are ‘back together,’ but the phrase is not really meaningful.”

Lowell died of a heart attack that September. Four years earlier Hardwick had written to him, “I feel that our marriage has been a complete mistake from the beginning.” Later, though, she would tell an interviewer — the words would be quoted in her 2007 obituary — “I didn’t know what I was getting into, but even if I had, I still would have married him. He was not crazy all the time — most of the time he was wonderful.”

Troy Jollimore‘s most recent book of poems is “Syllabus of Errors.”

THE DOLPHIN LETTERS: 1970-1979

Elizabeth Hardwick, Robert Lowell, and Their Circle

Edited by Saskia Hamilton

504 pages. Farrar, Straus & Giroux. $50.