Robert, born in Boston, the son of an English teacher, grew up in Massachusetts. He earned a bachelor's degree in classical studies and dance from Skidmore College, where he studied ballet. He took a degree in Greek and Latin at a New York University, where he was encouraged to train as a dancer. Robert went to George Balanchine's School of American Ballet. There in 1979 he was one of a few students hand picked by Balanchine to perform in Le Bourgeois Gentilhomme, a work the Russian-born choreographer created for Nureyev.
Nureyev and Robert met on the way to rehearsal. Robert, who knew Nureyev had recently visited Egypt, asked him about the country. Nureyev asked him where to buy batteries for his ghettoblaster. After the rehearsal and further chat, Nureyev asked him for tea at his New York hotel suite that afternoon. They ended up in bed.
Nureyev asked him to phone next day. Robert thought he was joking. A day or so later at rehearsal, Nureyev asked why he had not phoned. Robert looked at him in amazement. They went out together for three evenings, then Robert moved into Nureyev's New York apartment, where he stayed until evicted fourteen years later, after Nureyev's death, treated, as he said, "like a lackey". Nureyev introduced him proudly to his circle. "This is my young friend, Robert Tracy."
Nureyev's friends were relieved to see him with a young man who was not a hustler or rough trade, someone who could converse over dinner. He became Nureyev's social organiser and secretary as well as companion. Nureyev and Robert were both diagnosed with the AIDS virus in 1983.
Robert was the most durable of Nureyev's live-in companions. They were together, with only a break of eight months, until shortly before the dancer's death in 1993. For the first two-and-a-half years they were lovers - a long time by the standards of Nureyev's highly promiscuous and professionally driven life.
Nureyev made no will. He left an estimated $33m to a foundation named after him. Under an agreement with the foundation which recognised his entitlement to some security after the long relationship, Robert received $600,000, paid in instalments. One condition was that he did not talk publicly about the relationship.
The agreement lapsed, but Robert remained in seclusion in New York, teaching dance history as an associate professor at Fordham University and publishing well-reviewed books. He lately worked on a study of the dancer, choreographer and director Alvin Ailey.
Robert's first book, "Balanchine's Ballerinas: Conversations With the Muses," was published by Simon & Schuster in 1983 and described by The Wall Street Journal as "this year's great ballet book." Subsequent books included "Goddess: Martha Graham's Dancers Remember" (1997) and "Ailey Spirit: The Journey of an American Dance Company" (2004), both published by Limelight.
He also edited Nigel Gosling's "Prowling the Pavements: Selected Writings From London, 1950-1980" (Winchell, 1986) and contributed to Isamu Noguchi's 1994 anthology "Essays and Conversations" and to the International Encyclopedia of Dance. He also wrote on dance, theater, music, art and film for newspapers and magazines including The New York Times, Vanity Fair, Dance, Elle and Vogue.
Robert died because of complications of infection with H.I.V.