Justin Timberlake, who was arrested for driving while intoxicated in the Hamptons on Monday night, has allegedly struggled with a hidden drinking problem for years, RadarOnline.com has learned. “It’s not a secret. Everyone knows,” a music insider told Page Six after news of the singer’s arrest broke on Tuesday. “He has a real drinking problem, a lot of weed — but a major alcohol problem.” “He’s been hiding and masking it for years,” the source claimed, adding that “everyone around him have been enablers” and that Timberlake’s drinking finally “got to him.” “It’s a real thing, and when you have…