Edwards, a former U.S. senator from North Carolina, issued a statement late Wednesday, calling the separation "an extraordinarily sad moment."
"I love my children more than anything and still care deeply about Elizabeth,” he said.
The separation comes as details of John Edwards' affair with former campaign staffer leak out in advance of a tell-all book by longtime aide Andrew Young.
Young says in his book that Edwards told him he thought about leaving his wife but also cited his love for her as a reason to keep details of an affair hidden, according to The Wall Street Journal .
The Journal reported on its Web site that Andrew Young says Edwards asked him to go into hiding with Edwards' mistress, in part because of Elizabeth Edwards' health.
Young's book, "The Politician," is not due out until Saturday, but the The Wall Street Journal said it purchased a copy Monday at a Washington-area book store.
Elizabeth Edwards released a statement through her publisher, Random House, that said she "is moving on with her life and wants to put this difficult chapter behind her. It was an excruciatingly painful period for her, and she no interest in rehashing the past."
Young wrote that John Edwards concluded "that if I helped him, I would make Mrs. Edwards' dying days a bit easier. 'I know you're mad at her, Andrew, but I love her. I can't let her die knowing this.'"
Elizabeth Edwards was first diagnosed with breast cancer in 2004, and after a brief remission, the cancer returned in an incurable form in 2007.
John Edwards acknowledged for the first time last week that he fathered a child with Rielle Hunter.
Elizabeth Edwards believed Young fathered Hunter's child until John Edwards confessed to her last summer that he was the father, according to the statement issued by Random House.
Young's book says Hunter visited the Edwards' home and played with his two young children while Elizabeth Edwards was on a book tour. John Edwards promised to marry Hunter, a videographer hired by the campaign to produce promotional videos, and that the Dave Matthews Band would play at their wedding reception.
Two wealthy Edwards supporters, Texas attorney Fred Baron and Virginia heiress Rachel "Bunny" Mellon, provided money to Hunter, according to the book. Baron, who died of cancer in 2008, was finance chairman for the Edwards campaign.
A federal grand jury has been investigating for months to determine whether campaign funds were used to hide the affair. Both Young and Hunter – she had her young daughter in tow – have appeared at the federal courthouse in Raleigh on days when the grand jury was meeting.
Young provides an unflattering portrait of Edwards, talking about his obsession with campaign donations, his fixation with his hair, his disapproval of "fat rednecks" at state fairs and the lengths he went to to hide the affair, including trying to get Young to persuade Hunter to have an abortion.
Young has said in excerpts of an ABC News interview that Edwards asked him to find a doctor to fake a paternity test and to steal a diaper from the baby to secretly do a DNA test.
The book describes Young's discovery of a videotape showing Edwards and a naked Hunter.
"It was like watching a traffic pileup occur in slow motion – it was repelling but also transfixing," he writes, according to the Journal.
Elizabeth Edwards said in the Random House statement that the book contains "many falsehoods and exaggerations," and she called Young's contention in the book that she tried to politicize her cancer "unconscionable, hurtful and patently false."
Young lives on a secluded estate in Orange County with his wife and three children.
Edwards has largely stayed secluded since first admitting the affair in August 2008. He spent part of last week in Haiti helping with relief efforts.