Paris Hilton and Britney Spears won't be co-hosting the Billboard awards next week after all - Spears has reportedly backed out of the job. "She pulled out," said a source. "She didn't give a reason." Reps for Spears and Hilton have yet to comment, but an insider at Fox says, "We really don't know the reason. But we're disappointed she backed out." Spears and Hilton have been inseparable for the last week, partying all over LA. "I love her," Hilton told US mag while shopping in Malibu on Monday. "She is the sweetest girl I know. She's so down-to-earth. I just want to make her smile and be happy."