At the Mercy of My Vampire Ex.

Three years ago, she pushed her husband into the rain, making him hate her enough to survive. Three years later, she escapes into the Underground Blood City, only to find its ruler is him—the man she "killed" is now a vampire godfather. He traps her by his side, punishing her with hatred, binding her with a blood oath, until he discovers the truth: she never betrayed him. She left to save his life.