Marc Jacobs, fresh out of rehab, has gone running back into the arms of his party-hardy rent boy, Jason Preston. The fashion designer is so besotted with Preston, who had Jacobs’ name tattooed on his arm the first month they started dating, that he’s followed suit. Spies say Jacobs now has the initials “JP” permanently inked above his navel. It’s probably a bad idea since the fiery couple broke up several times last year. We’d have called Jacobs for comment, ...