Garland would marry five times in her life before her death at the age of 47 from an overdose of pills.
Luft also wrote about Garland's struggle with drugs, something he blames for her many suicide attempts throughout their relationship.
"She was married to the drugs before she met me, and she never really got divorced,' said Luft.
"Judy admitted she felt she grew inches when she took Benzedrine."
The details of her dependence will all be included in his book Judy and I: My Life with Judy Garland, which is due out in March.
Luft also wrote about the magnetism between himself and Garland when the two first met, and how shocked he was after their initial night of passion.
"It was virtually impossible to be cool around Judy since I lusted so entirely after her," said Luft of first meeting the star, who at that time was still married to her second husband and daughter Liza's father, Meet Me In St. Louis director Vincente Minnelli.
"I was to discover just how different Judy was from other women. She was uninhibited, giving herself over to her passions so completely."
At the time Garland's career was fading, but Luft turned things around, and during their 13 years together she found immense success while also being nominated for two Academy Awards for her roles in A Star is Born and Judgment at Nuremberg.