BEIJING -- An Asian American who is one of the biggest pop stars in China apologized to his family and fans on Monday and said he will take a break from performing after a public dispute on social media with his ex-wife, who accused him of infidelity and hiring prostitutes.The dayslong back-and-forth has riveted fans of Wang Leehom, who is popular across the Chinese-speaking world and has acted in movies including “Lust, Caution” in 2007.