"Both of Us: My Life With Farrah" was released on Tuesday by Random House imprint Crown Archetype.
O'Neal spoke about his memoir with Matt Lauer on the Today Show on Tuesday and said that writing the book was "a way to stay close" to Fawcett, who died of cancer in 2009 at the age of 62. The two were involved in a romantic relationship for many years, one that produced a son, Redmond O'Neal, who has been in the headlines because of ongoing drug problems.
"I wrote it because I missed her," O'Neal told Lauer. "And it was a way to keep the line between us going. I still felt she was nearby when I wrote this. She was close."
Soon before Fawcett died, O'Neal revealed to Barbara Walters that he and Fawcett would get married as soon as Fawcett was able. She died before this could happen. He told Lauer that he was always proposing marriage to Fawcett.
"For 18 years, I asked her to marry me," he said.
O'Neal also told Lauer that he didn't think his late partner would be upset with the memoir: "She would be glad I was working on something, even if it was our relationship, which was imperfect of course but aren't they all?"