Jack barely glanced at the $827 bill before shoving it at his girlfriend, Lora. “Your turn, babe,” he said. But this time, Lora refused—trembling, near tears. And as their waitress, I’d seen enough. When they first came in, Jack and Lora seemed happy. But over time, he started ordering lavish meals—for himself and his friends—while Lora paid quietly. She barely...