LeAnn Rimes Reveals Why She Cheated on Husband

"I need to hit things."

LeAnn Rimes used to be America's sweetheart, and now she's the poster woman for dirty no-good cheaters. So how does the country star live with herself? Lot's and lot's of crunches.

Read: Details of LeAnn Rimes Marriage Scandal

Rimes, 28, is on the cover of the latest issue of Shape Magazine, and inside she reveals the reasons behind her much-publicized divorce from backup dancer Dean Sheremet (who she famously cheated on with current beau Eddie Cibrian).

"My relationship with Dean was great, but ultimately it wasn't a fulfilling marriage for either of us," Rimes says. "We got married so young: I was 19 and he was 21, so as we got older, we grew apart."

As for the whole affair thing, Rimes acknowledges she lost a lot of fans because of her actions.

Read: LeAnn Rimes Tweets About Shot in the Butt

"I understand why people are disappointed in me, especially since I grew up as America's sweetheart," she says.

Still, Rimes says the publicity really took a toll on her, and that through exercise she was able to feel better about herself.

"Sometimes I felt so depressed I didn't want to get out of bed, so just getting to the gym—even for a few minutes—was a big accomplishment," she says. "It really did make me feel better and kind of saved me. It gave me a bit of sanity. Even now, on days when I'm really frustrated, I'll walk into the gym and say to my trainer, 'We're boxing today. For an hour. I need to hit things.'"

Read: Eddie Cibrian Fired From CSI

On second thought, maybe Sheremet is better off without her.

Rimes can be seen in the October issue of Shape Magazine, which hits stands September 20.