Calvin Klein’s ex-boy toy Nick Gruber says the designer took extreme measures when he once wrongly suspected Gruber of cheating during a 2 1/2 -year relationship. “[Calvin] . . . drove me down to the Holiday Inn in Chelsea,” Gruber says in Page Six Magazine, out today. “We went downstairs in the basement of the hotel.” Gruber says another man was waiting with a lie detector. The stranger further told Gruber, 48 years Klein’s junior, he was an ex-detective and presented him with a business card reading simply, “Dr. Love.” “He made me take a lie-detector test,” Gruber says. “I passed it . . . But I mean, what kind of partner would make you take a lie detector test? I was like, ‘Did you ever cheat on me, Calvin?’ I never cheated on him.” Gruber also says Klein bought him a $250,000 Bentley, but, “When we broke up, he took it back.”