The 29-year-old English popstar split from the Chelsea and England defender in 2010 following claims that he had cheated on her with other women.
"It takes a long time after you've been with someone as long as I was [with Ashley] not to feel like you're cheating on them," she said.
"That may sound crazy, but it's the way I felt after him. I had completely committed myself."
Cheryl and Ashley were married for four years.