My husband’s mistress rang the doorbell, handed me her coat, and said: “Tell Stephen I’m here.” She thought I was the maid. In my own house. She didn’t know I had been his wife for 12 years, nor that I was the owner of the company where her father worked. Twenty minutes later, Stephen walked in. By nightfall, he was packing his bags. And three weeks later, I made a call that would cost him everything…