John Mayer & Jessica Simpson Wedding Bells?

Jessica Simpson, 26, could overtake ex-husband Nick Lachey and his girlfriend of one year, Vanessa Minnillo, in the race to the altar reports Star Magazine.

Her on-again romance with singer John Mayer, 29, is so hot that the couple was reportedly seen checking out diamond rings at Cartier on March 8 during their six day trip to Rome!

And John has been telling friends “she’s the one he wants to settle down with,� says a source.

“He says, ‘she has all the right ingredients, and she makes me laugh.’� It’s an unlikely pairing, but apparently he’s found his soul mate: He wanted to have “a wife, a home, a degree of stability� before he turned 30- just six months from now!- says the source. “The clock is ticking for him!� Expect a low-key proposal and a traditional, intimate wedding when their schedules clear up, adds the source.

In other news, Jessica Simpson and John Mayer continued their love tour with a late-night bite at Hollywood hot spot Citizen Smith on Monday reports E Online

Along with a group of about a dozen friends, Simpson and Mayer dined on mac & cheese, Buffalo Smith wings and a frozen hot chocolate.

The lovebirds were "very into each other" for the entire couple of hours that they were there reports E!.