"I just told her I was going to get some help," the 41-year-old says of his decision to enter rehab shortly after he publicly apologized for cheating on Bullock, then his wife of five years.
In his first TV interview since the scandal, the Monster Garage star also said his Oscar-winning wife was suspicious before he apologized for "poor judgment" and asked his wife and children for forgiveness.
"I think she's had her suspicions in the past, but, you know, I lied and lied my way out of it," James says in the interview. "I lied to everyone about everything, even to myself."
Since his public mea culpa and stint in rehab, Bullock filed for divorce in April and announced that she had adopted a 3 1/2-month-old baby boy as a single parent.
In the interview, James also discusses the criticism he received after being photographed wearing a Nazi hat while in rehab. "I could tell by the look on my face [in the photo] it was a joke that was funny then, probably for a minute. But then looking at it in the context of now and in my life, it's not funny," James told Nightline. "There's not a racist bone in my body."
James said the controversy surrounding the hat only made it that much more difficult to cope with the demise of his marriage. "Dealing with losing my marriage and my son and embarrassing everyone and decimating my life ... to be called a racist on top of that is, it makes me really sad."
James' Nightline interview airs Tuesday at 11:35/10:35c on ABC.