Throwing it back.

After 11 years, Jessica Simpson is sounding off on her 2009 split from former Dallas Cowboys quarterback, Tony Romo, ending their two-year relationship.

“[Tony] accused me of seeing John [Mayer] behind his back,” Simpson, 39, wrote in her new memoir, “Open Book,” out Tuesday. “I hadn’t cheated on Tony at all. But I could not lie and say I hadn’t even seen [Mayer].”

Simpson says that she was at her folks’ house when she ran into her then on-and-off beau Mayer, 42, who emailed her about the run-in, which 39-year-old Romo found.

Though she insisted that “nothing happened,” the footballer “didn’t believe that for a second” and “broke up with me right there.”

As the breakup “would imply that he wasn’t enough for me,” Simpson was confident Romo wouldn’t dish on it to the public, though he soon came to his senses and realized she’d been honest, but the “breakup had been so ugly that it shocked me into realizing it had been necessary.”

At the time of the split, Simpson said Mayer had been bucking for their own reunion, “practically asking my parents for my hand in marriage while I was in a serious relationship” and “swearing to me up and down that he was a changed man.”

By the time Simpson was single, she realized that, “All this time, all those years, he was breaking up with me to torture himself enough to get good material.”

The pair kept in touch for months, as Simpson said, “it felt inevitable to be in love with John,” but she “knew now not to let him get close enough to shoot me down again.”

In her book, Simpson also discusses her first marriage, to Nick Lachey, which ended after three years in 2005.

“I obviously haven’t read the book, so I don’t know what she said or what she revealed there,” Lachey, 46, said while appearing on “Today” Monday with wife Vanessa. “Certainly happy for her and her life, I know she’s happy for us. There’s definitely a mutual respect there. Obviously it was a long time ago. We’ve all moved on.”

Vanessa did clear up that they were not the ones who sent Simpson a gift after she had children.

“I don’t know her address,” she said. “But thank you, whoever sent it from us!”