08/24/2006 at 01:00 PM EDT
He may have five Grammys to his name and have sold 15 million copies of his latest album, Confessions, but Usher says his new starring role in Chicago on Broadway requires a whole new level of commitment.
"Broadway is like a monogamous relationship," the R&B star, 27, told PEOPLE during a party to celebrate his debut as singing shyster lawyer Billy Flynn in the long-running revival of the musical. "Doing anything else, like acting in Hollywood – which is great – it's like a one-night stand. You do it and then you keep moving."
The role of Flynn was originally created in the 1975 production by Jerry Orbach – long before the late actor became a household name on TV's Law & Order – and then played by Richard Gere in the 2002 Oscar-winning best picture.
Usher, whose opening night this week brought out stars Penelope Cruz, Gabrielle Union, Clive Davis, and Rosie Perez, among others, will be sporting Billy's tap shoes until Oct. 1.
As for how she liked seeing her son making his Broadway bow, Usher's mom, Jonetta Patton, told PEOPLE: "I thought his performance was unbelievable. Absolutely incredible. I am so so, so happy."