Eric Johnson Cheating On Jessica Simpson With Ex-Wife?

Is Jessica Simpson in another bad relationship? 

Her fiance, former NFL player Eric Johnson, allegedly slept with Simpson and his ex-wife Keri Johnson at the same time.

But this isn't that surprising since Eric was still married to Keri when him and Simpson met at a mutual friend's house in Los Angeles. Eric even brought Keri with him as his date!

When the football player and singer met, the couple was already on a break, but it didn't "make their marriage stronger," a friend of Keri's told Star magazine.

Instead of trying to work on his relationship with his wife at the time, he dived right into a relationship with Simpson. 

"He's a two-timing cheat!" one of Keri's friends told Star. "He was still having sex with Keri after he started seeing Jessica. She needs to think twice before marrying him. He's already cheated on her once - he'll most likely do it again." 

Even though Simpson and Johnson recently welcomed their daughter Maxwell, they're in no hurry to walk down the aisle. She told talk show host Katie Couric they hadn't set the date yet for their wedding. 

"It won't be this year," she told Couric. "I really want to do a big, fun wedding with my friends and family."  

Simpson has been criticized for her pregnancy weight -- the fashion designer weighed as much as 170 pounds -- but she is now 10 pounds away fom her pre-baby size.

"My body is not bouncing back like a supermodel," Simpson told USA Today. "I'm just your everyday woman who is trying to feel good and be healthy for her daughter, her fiancé and herself."

In her Weight Watchers commercials (Simpson is the latest spokesperson), she says, "There is a lot of pressure to lose weight, but I'm not a supermodel. I'm just Jessica trying to eat real food in the real world."