"It was among the dumber ideas I think I've ever seen executed in history," said the singer, in an appearance Wednesday on "Late Show With David Letterman."
"For a while we actually enjoyed doing the show," he added, "(but) it just got to a place where it was so invasive, it became a problem."
Simpson and Lachey were divorced on June 30, 2006, after almost three and a half years of marriage. Their reality show ran for three seasons.
Lachey said that it's too soon after the breakup for him to determine exactly what caused the end of his marriage, but he does think that being under the scrutiny of the reality show's cameras was certainly a factor.
So, are they friends now?
"I think both of us have handled it about as well as we possibly could under the microscope that we're under," he said. "I think, with time, it will give us a better opportunity to redefine our relationship."
His latest album, "What's Left Of Me," includes the singles "I Can't Hate You Anymore" and "Resolution," in addition to the title track.
"The new album was certainly inspired by a lot of what I was going through in my personal life," said Lachey.
Despite the very public split, Lachey hasn't given up on romance.
"It hasn't squashed my concept of love or marriage," he said. "I think that certain situations are meant to work out and others aren't, and unfortunately, this one wasn't."
Lachey said he's moved on and is dating but has decided to learn from the past and keep his private life private.
Lately, he's been frequently photographed with television personality Vanessa Minillo, who appears in the video for "What's Left Of Me."
By Judy Faber