The Boyzone star cheated on the model with a dancer in 2010. The couple officially announced their split in April this year.
Speaking to Piers Morgan for a future episode of Life Stories, the singer revealed how his marriage ending "crushed [him] - a part of [him] died".
According to The Sun, he said: "The pain that I caused Yvonne has been devastating. I felt I'd lost everything because of what I had done.
"I spent so long doing everything right, and then to do what I did and for it to be such a big deal - it just floored me. I'll never do this thing again and be the best I can be."
When asked how he felt about her new relationship with cinematographer John Conroy, he added: "I still love her. I was happy she was happy."
Keating also admitted that he visited a psychiatrist to help him get over the split.