Warren Buffett, the world's richest man, admits he made a poor choice. No, not that he didn't invest more in Google than Microsoft, but that he didn't work harder on his relationship with his late wife, Susie, the mother of his three children.

"The biggest mistake I ever made was letting her walk out the door," he says.

As with many separations, Susie was driven to it.

Buffett, 78, who spent hours and hours talking with the author Alice Schroeder for the book The Snowball, regrets that he gave Susie so many reasons to leave, say Rush & Molloy in The Daily News.

One was Katharine Graham, publisher of The Washington Post, and Newsweek. Buffett was 46 when Graham, then a 59-year-old widow, became smitten with him. They spent time at her Martha’s Vineyard home and traveled widely.

What is surprising is that Graham's own marriage was ruined by her husband’s infidelity. And who knew before this book that Katharine Graham was one of the early cougars? (While we at FWW approve of dating someone who's fabulously younger and cute, it is verboten to date a married man no matter what his age.)

Graham, it turns out, was pretty open about the affair with Buffett, and was seen tossing her house key to Buffet at parties. Schroeder writes that Susie "made it plain to several friends that she was furious and humiliated," but reports that she sent Graham a letter granting her permission to date her husband.

"Kay showed the letter to people as though it let her off the hook," Schroeder says.

Naturally the humiliation at home marinated into resentment.

When Buffett was at home in Omaha, the book says, he spent most of his time in his study and didn't make enough effort with Susie. Telling one of her friends he was an "iceberg," Susie began a romance with her tennis coach, John McCabe. Then, in 1977, after falling in love with the arts scene in San Francisco, she informed her husband that she was buying a small apartment there.

McCabe followed.

But Susie, like many wives, still cared about her husband. (A recent example of that, how Shanna Moakler rushed to her ex’s, Travis Barker’s, side after his plane crash.)

And so she arranged for an attractive blond, Astrid Menks, to work as his housekeeper.

Menks eventually moved in with Buffett, even though he and Susie never divorced. After Susie’s death in 2004, he married Menks.

Buffett tells Schroeder that Susie's departure "was preventable.”

“It was definitely 95% my fault. ... I just wasn't attuned enough to her, and she'd always been perfectly attuned to me. She kept me together for a lot of years ... It shouldn't have happened."

There is a part of me that just wants to shake guys like a pair of dice. They just don't realize how good they have it until the wife is gone and the trust is shattered. They roll the dice and, surprise, the next one isn't as good.

One time I interviewed Raoul Felder, the famous New York divorce attorney. I asked him how the second wife compared with the first. "In the beginning, the guys are excited to be with the new girlfriend-wannabe new wife," he said. "But then after about six months, they start to miss what they had before. But often the damage is already done."

Buffett not remarrying until after Susie died was an unspoken compliment to his wife. She would be his wife always — even if he couldn't have her.

Here’s a lesson, guys: Work on appreciating what you have, because emotional riches are often far more valuable and precious than financial ones.