Gwen Stefani 'Went Through Months and Months of Torture' Before Gavin Rossdale Divorce

Gwen Stefani was in “Misery” before new beau Blake Shelton came into her life.

The No Doubt singer split from Gavin Rossdale last year. Shortly after, PEOPLE confirmed reports that the divorce was triggered by the Bush rocker’s infidelities with the family’s longtime nanny.

While neither of the exes have addressed the specifics of the scandal, Stefani opened up about grieving the end of their marriage in the new September issue of Cosmopolitan.

“Nobody except for my parents, the people involved, and whoever they told [know specifics],” the singer, 46, told the women’s lifestyle glossy. “Nobody would believe it if I could really say what happened. I went through months and months of torture.”

When asked if she knew something was going on with Rossdale, she replied: “All you have to do is listen to every single song I’ve ever written and it’s all there. It’s an ongoing theme that I’ve had for a long time.”

Stefani is in a happier place these days, dating country star Shelton since the fall. The singer chronicled the end of her marriage and her blossoming relationship with Shelton in her new album This Is What the Truth Feels Like, and the couple even wrote and recorded a duet, “Go Ahead and Break My Heart,” which appeared on his new album, If I’m Honest.

“We were both having trust issues, as you would if you were us,” Stefani said of writing the track. “It was like, ‘I have so many problems. How can I now be getting into another potentially huge problem? What am I doing?'”

But the emotional track came together organically.

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Added Stefani: “Blake wrote the song and sent it to me. He was like, ‘Help me finish it.’ I wrote a verse and sent it to him, but he was gone because he doesn’t live in L.A. He didn’t have Wi-Fi, so he wasn’t answering me back! As soon as he came back to town, he brought his guitar over. We were like, ‘We wrote a song together! This is crazy!'”

As for their on-screen romance, which played out when they were both coaches on NBC’s The Voice, Stefani says the show played it up as a storyline before they even began dating.

“We were laughing our heads off when we saw the blind auditions. I love NBC, but they for sure edited stuff to look like we were flirting,” she told Cosmo. “They chose to run with that story before anything was even real. I hardly knew him. But it was like it was in the air – happening before it happened.”

While Stefani and Shelton’s relationship continues to heat up – a source recently told PEOPLE, “Everyone is expecting an engagement” – she and Rossdale continue to share custody of their three sons, Kingston, 10, Zuma, 7, and Apollo, 2.

“He’s doing great and staying focused on music and the kids,” an insider recently told PEOPLE of Rossdale, 50, who is putting the finishing touches on a new Bush album. “When he’s not performing, Gavin spends his time with the kids. He knows the situation hasn’t been easy for them, and he’s with them as much as possible. They’re his life.”