Macbeth and Lady Macbeth are faced with becoming evil as a result of their evil actions, and it destroys each of them eventually.
In Act 3 and 4, Macbeth and Lady Macbeth’s actions start to catch up to them. In the previous acts, Lady Macbeth has spurred Macbeth into killing Duncan so that he can become king. Yet by Act 3, she realizes she has created a monster when he is no longer talking to her.
Be innocent of the knowledge, dearest chuck,(50)
Till thou applaud the deed. (Act 3, Scene 2)
She is not happy that he is not telling her what is going on, because she thinks he is up to something. He is up to something! He is planning a few murders to coincide with his new power.
To be thus is nothing,
But to be safely thus. Our fears in Banquo
Stick deep, and in his royalty of nature
Reigns that which would be fear'd. (Act 3, Scene 1)
Once Macbeth begins killing, he does not seem to be able to stop. He also sees Banquo’s ghost at his banquet, causing concern and embarrassment to Lady Macbeth. She makes excuses for him, but she is concerned that she can no longer control him. Without her knowledge, he also has Macduff’s entire family killed. This eventually is too much for her, and Lady Macbeth cannot live with the guilt of what she created.