The couple announced the break-up in August and Stefani has now moved on to romance country singer Blake Shelton, a fellow judge on US TV talent show "The Voice".
"There's so many bad things... Oh my God, I can't even believe it. I wish it didn't happen. I wish that it all wasn't happening, but at the same time, I feel like it was part of my life journey.
"In my life, I've had two really bad heartbreaks, and I've written some incredible music out of it.