After Duncan's murder, there are definite changes in Macbeth as he becomes more paranoid and intent on assuring the witches prophesies for himself. Having been so unsure, even after Duncan's murder when he was confused and racked by guilt at having killed his king, he is encouraged by Lady Macbeth to "wash " his guilt and fears away because"a little water clears us of this deed" II.i.
In Act III then, he seems almost unstoppable, arranging for Banquo to be murdered and even though he is tormented by Banquo's ghost and he "hath murdered sleep," he is still driven by his ambition and the need to control the situation.
He will reach his goal through the quickest, though not the most honorable, route
although, interestingly, Lady Macbeth is not able to assuage his fears. She does cover for him though, explaining that he has had problems since he was a child and that guests must not worry as he rants about Banquo's ghost.
When Macbeth has left to fight MacDuff and Lady Macbeth is left alone, their relationship deteriorates. Lady Macbeth experiences hallucinations and insomnia but,rather than driving her to more murders, she becomes remorseful and even scared. It will eventually drive her insane.
The deterioration of the Macbeth's relationship that began in Act II after Duncan's murder is intensified and
she is now excluded by her husband from partaking in either the natural or the supernatural progression ahead.