The Peckham-born host of BBC One's cookery competition, who met his third wife Heidi Brown over Twitter, admits that he remains in "love" with her and is shocked by the situation.
"Oh God, I can't believe this has happened," he told the Daily Mail. "I just really don't know what to do - we talk to each other three or four times a day.
"She says she will always be there for me - we have a really strong relationship. She wants to continue as my PA - she says she'll work for me for the next 30 years."
"I've had a terrible week. It's all over Twitter," a downbeat Wallace went on. "I'm in bits, I love my wife. I don't know what's gone wrong. She's an amazing woman."
Explaining why they split, the 47-year-old recalled: "It's all gone mad. It went wrong about three months ago. We knew there was something wrong. We want different things.
"We both have images of each other, I don't know if they were right. I had an image of her and she had one of me but whether they were right..."
Admitting to his own mistakes, he confessed: "I'm an awkward bugger, I'm demanding. I like working and making money. I'm driven, I'm here all the time. I'm always busy, I'm always trying to build the business, do the TV.
"I live round the corner and Heidi lives in Whitstable with my kids. She's never been interested in fame, she didn't like coming to red carpet events. She hated all that. People thought she was, but nothing's further from the truth.
"She's happiest walking our dogs, a rescue greyhound and a whippet, on the beach. That's all she wants - a quiet life, that's where she's happiest.
"Heidi is brilliant. We always joke that she's more mature than me - she says she's an old woman in a young woman's body."
Meanwhile, Wallace insisted that he is "done" with relationships, adding: "It's really weird, they're giving me the come-on but I'm not interested. That's it for me - there's no other woman. [Heidi]'s beautiful, absolutely stunning."
Wallace's MasterChef partner John Torode separated from his wife of four years in January.