Couples

Balthazar Getty's Wife 'Humiliated' by His Affair with Sienna Miller

07/17/2008 at 07:40 AM EDT

Sienna Miller's steamy affair – and much of her body – has been exposed now that the barely clad actress has been spotted kissing married Balthazar Getty in a boat off the Amalfi coast.

Miller, who had a roller-coaster relationship with Jude Law and broke up with actor Rhys Ifans only weeks ago, has been quietly dating Getty for "at least two months," said a source.

Miller, sporting a sailor's cap, was also spotted topless on the balcony of an Italian hotel room kissing Getty. Meanwhile, the Brothers & Sisters actor, 33, and his wife Rosetta "have been living separate lives for a while," a source tells PEOPLE.

Getty, who has a tattoo of his wife's name on his chest, married Rosetta in May 2000. They had their fourth child together 10 months ago.

"It's humiliating," a friend tells PEOPLE. "Rosetta left the country to protect the kids, and he continues to see Sienna publicly."

The two met through Getty's Brothers & Sisters costar Matthew Rhys. Rhys, who briefly hooked up with Miller, was livid when the photos of the couple surfaced, says a source.

For more on Sienna and Balthazar's romance, pick up this week's issue of PEOPLE, on newsstands Friday.