To be precise, Muzan doesn't feel any affection to his wife, he just chooses his wife to be at his side. He's a demon and cannot feel no longer affections of love but anger and revenge, his obsession through finding the Blue Spider Lily, a flower that can cure him and be able to conquer the sun. Muzan doesn't love his wife, he chooses her to be at his side since he finds her amusing and a useful woman.