Excerpts from the interview, printed in Wednesday's USA Today, included Lachey saying: "I'll tell you how I knew my marriage was over: I was told."
He went on to say the couple grew so accustomed to their roles on the MTV reality show "Newlyweds," they began "playing these parts even when we were by ourselves."
"It became a really blurred line," he said. "There was a question about what truly was our reality."
Lachey said he did not know whether his wife cheated on him with other men, but if she did, "it was the result of something bigger."
"Sometimes I think it would be easier if I had just walked in the house and found her in bed with a guy," he said. "That would be clear-cut. End of story. I wouldn't have to deal with the uncertainty of adultery."