How has the pearl caused the relationship of Juana and Kino to fall apart?

The pearl consumes Kino. Juana sees this but is powerless to do anything about it. Kino became abusive when Juana tried to throw the pearl back into the sea. She believed it to be evil, and once she saw that Kino killed a man she felt that throwing it away was useless. Juana follows Kino but knows the pearl has consumed his heart.