Jessica Simpon, who can’t keep her men in place, is now jealous of Cameron Diaz for having a swell of a romantic time with John Mayer.

US Magazine says:

A source close to the singer tells Us Simpson is “really jealous” that ex John Mayer is seeing Cameron Diaz. “She had her mouth open a mile wide when she found out,” says the source. “She just freaked.” Simpson, 27, parted ways with Mayer, 29, in May after dating him on and off for seven months, and “she thinks about him all the time,” says the source. “She is so not over him.” Meanwhile, Simpson seems to be a distant memory for Mayer, who has continued his summer romance with Diaz, 35, in NYC. Though they spent August 22 and 23 apart (he hit the gym and recorded at a studio; she shopped and then lunched at Mary’s Fish Camp), they finally squeezed in quality time in the wee hours of August 24 at hot spot Socialista. The pair — who left at 4 a.m. through different exits — “were very cozy,” says a witness.

John Mayer may be a good singer, but he has awful taste in women. First, he dated this thing and fought with it in public, and now he’s on to this. So in this little triangle, the real loser here is John Mayer. It’s like you’re eating rotten meat and you’re jealous someone else is eating garbage.

Pics of Jessica Simpson going to a movie set in Los Angeles earlier this week (whatever movie it is, I’m sure it’ll suck):