"A Public Affair is a play on words," Simpson, 26, tells MTV News. "It's not about what you think it's going to be about."
Granted, she admits, "People probably expected (it to be about Lachey) because of everything going on in my life, but it's not about him at all."
Instead, she says, "It's about me going out with my girlfriends and forgetting everything that's around me, which is paparazzi, and just having a fun night. Because (paparazzi) can ruin a night."
That's not to say that Lachey didn't serve as the inspiration for at least one track on the album, Simpson reveals.
During the "really tough time" last year when things were falling apart, Simpson says she found solace when she shared one of her favorite songs with younger sister Ashlee: Patty Griffin's "Let Him Fly."
The song, which Simpson covers on the album, "is about how sometimes you just have to know when to let something go," she says. "(It) was just perfect for that moment. And I had to sing it."