How come Macbeth and Lady Macbeth aren't happy when they finally achieve their goal of becoming King and Queen of Scotland?
I'm trying to explain this but, im a bit confused as of why they aren't happy and need some help putting it into words.
I'd suggest that their guilt is destroying both of them as individuals and as a couple.
Lady Macbeth, who initially persuaded Macbeth to kill King Duncan but who does not do the deed itself because Duncan looks too much like her own father, is overcome with guilt over her part in the murder. The memory of all the blood she saw (because she had to retrieve the daggers that Macbeth left at the scene of the crime) prevent her from sleeping and later cause her to walk and talk in her sleep, reliving parts of the crime again and again. She has lost her husband, in that he no longer talks to her about important things, much less love, and she feels no joy in being queen.
Macbeth, while initially wavering about murdering Duncan, has become quite mad and is also no longer able to sleep. He has had to murder again (Duncan's servants) and has ordered the murders of friends and children in order to secure his throne. These murders, however, just make him worry more about who will try to take the crown from him. He can trust no one - and no longer confides even in his wife. He feels alone and recognizes that there is no way to recover what he once had, and his future looks grim, even if he has the power he once wanted.