Contractual Marriage to a Surly Duke

Reincarnation became a villain who poisoned her husband in a novel, but she was actually just a down-and-out young lady who was forced to contract marriage... If she didn't give birth to an heir, she would be driven away by her mother-in-law, and her husband who was sick and weak also kept her away from her. "We can pretend to be husband and wife, but we can't have children." Who is poisoning his husband? Selene is determined to investigate and help her husband recover. And in the process, her husband's attitude gradually changed?