K-Fed Concerned About Britney

During Britney Spears's recent wild weekend, her ex, Kevin Federline, canceled plans to party in Las Vegas during the NBA All-Star weekend in order to stay in Los Angeles to be available for the couple's children, sources tell PEOPLE. "Kevin is concerned for Britney and his children," says a friend of Federline's. "Of course he's concerned about her. He loves her. He's always loved her – even after she started divorce proceedings." The pair, who split in November, have two sons together, Sean Preston, 1, and Jayden James 5 months. According to another source, Federline had booked a room from Feb. 14 - 19 at the Venetian Resort Hotel Casino, but canceled the reservation. It's not clear if Federline has been in direct contact with his two sons or Spears, who voluntarily entered a rehabilitation facility on Tuesday. A rep for Federline could not be reached for comment.