Moore said her "codependency" on Kutcher led to "misguided" attempts to save their marriage, including threesomes.
"I don't think it should be implied that he instigated," Moore said of the threesomes. "He expressed something that was of a fantasy and [I agreed] in my efforts to want to please and be what I think he wanted.
"It was a misguided sense of not really wanting to look at the harder question or what was really missing," she explained. "Or in my case, because I really felt like I had created an addiction to him, that my co-dependency in a way I'd never had before, I'd never had that kind of attachment."
Moore discusses her relationship with Kutcher at length, including his alleged infidelity, in her memoir, Inside Out, released Tuesday.
"I put him first," Moore wrote. "So when he expressed his fantasy of bringing a third person into our bed, I didn't say no. I wanted to show him how great and fun I could be.
"They were good people, but it was still a mistake," she said of the experiences. "I was strangely flooded with shame, I couldn't shake the feeling that this whole thing was somehow my fault."
Moore told host Ellen DeGeneres she was somewhat "nervous" about naming people in her memoir, but said the the book is meant to give her point of view.
"I feel so good about the point of view. I have no interest in blaming or villainizing anyone," she said. "The journey in the book is about overcoming. In a sense, this is my story, my point of view. If anyone else in the book, including my daughters, if they see things differently -- and in some cases, they did."
Moore said she remains friendly with Bruce Willis, her second husband and the father to her three daughters, Rumer, Scout and Tallulah. She told DeGeneres she is not presently dating.