"When I was doing it, you know, one, I knew it was horrible, it made me feel horrible," James tells ABC's Nightline in an interview airing Tuesday. "And two, I knew I would get caught eventually, and I think I wanted to get caught. ... It was me trying to self-sabotage my life."
Asked why he'd hurt someone who was – and he says still is – the most important person in his life, James is at a loss for words. "It's hard for me to talk about, a little bit, because I still really love her and care about her," he says.
But the West Coast Choppers owner, 41, is under no illusions about the level of that hurt. "I've spent my whole life with the kids and with her trying to ... protect her from everything, but the most hurt she's ever been caused is by the person that wanted to protect her," he says.
In an earlier promo for the show, James admits: "I took a pretty amazing life and marriage ... and threw it away."
Allegations of James's infidelity emerged shortly after Bullock, 45, won an Oscar for her leading role in The Blind Side in March.
In the Nightline interview, James will also address whether Bullock knew anything about his affairs, what he really went to rehab for, and what role – if any – will he play in the life of Bullock's adopted son, Louis.