Credit: Jason LaVeris/FilmMagic; Beck Starr/FilmMagic

There were barely any celebrities at West Hollywood hotspot Villa the night of November 19 -- which might be why Lindsay Lohan and Cash Warren immediately gravitated towards one another.

Film producer Warren, 30, was partying without Jessica Alba, his wife of one and half years and mom to his daughter Honor, 18 months. "When he goes out with friends, he gets into trouble," a pal says of Alba's husband in the new issue of Us Weekly.

Indeed. Soon after discovering one another at Villa, Warren and Lohan "ignored friends and just chatted." The real trouble began half an hour in. "Lindsay and Cash started making out," an onlooker tells Us.

"Lip on tongue," the eyewitness continues, "It was raw. They were not shy!"

Another Villa patron that night gasped, "It was a shock to see the two of them kiss, but it was real."

For her part, Lohan tells Us that the account is "absurd. He is married. I wouldn't dare kiss him."

But pals of both Lohan and Warren -- who share a love of nightlife -- insist otherwise. Those close to Warren and Alba worry that their marriage is already on shaky footing. "Jessica is not as into Cash as she used to be," one source says.

And the ever-fragile Lohan "becomes easily attached to everyone she meets and gets close to," one friend says. Adds another: "she's falling for [Cash]."

To read more about Warren and Alba's arguments, Lohan's Twitter-obsession with Warren and more, pick up the latest issue of Us Weekly -- on newsstands now!