Dexter Peebles may be a 29-year-old St. Louis boy, but his alter ego, Cheyenne Devereaux, is a Southern belle relatively new to town. “Before, she was just mine,” says Peebles. “Now, sharing her with other people is incredibly freeing.” Photographed by Susan Bennet in her studio on Lemay Ferry Road, Devereaux danced to Florence +…