If the accused wasn't responsible ...

She'd been accused of poisoning her first husband. People in the town believed she got away with murder. So when he is getting older, instead of accepting it, he thinks she is trying to kill him too. He probably knows in his heart it's not true, which is why he won't let the doctor actually examine him.

He's also a mean old man, as evidenced by how he responded to his daughters when they did show up to see him. I wouldn't have been surprised if part of it was him having fun manipulating everyone.