When, why and how do Macbeth and Lady Macbeth start growing apart?
In the beginning, Macbeth depended upon Lady Macbeth for his motivation. Macbeth had changed his mind about murdering King Duncan:
We will proceed no further in this business.
He has recently honored me,
When Macbeth had changed his mind about the murdering of King Duncan, Lady Macbeth influenced him to follow through with the murder:
Are you afraid
To be the same man in reality
As the one you wish to be?
Macbeth agreed to follow through with the murder, claiming that Lady Macbeth had convinced him to proceed with the terrible event:
I’m convinced, and I commit
Every part of my body to this terrible event.
After the murder, Macbeth began to take charge. He no longer depended upon Lady Macbeth for courage. He began planning Banquo's murder without sharing his plans with Lady Macbeth. Although she knew he was planning something, she did not know exactly what Macbeth was planning. Macbeth talks in riddles of his fear of Banquo:
We have crushed the snake, but we haven’t killed it;
She'll recover, and be herself, while our poor evil-doing
Remains in danger of her poisonous bite.
Here, Macbeth is referring to Banquo. Since Banquo heard the witches' prophecies to Macbeth, Banquo is a threat. Here, Macbeth is contemplating the murder of Banquo. He does not seem to need Lady Macbeth's influence. Macbeth is taking charge of the situation without the influence of his dear wife.
Macbeth is in torment for what he has done. He and Lady Macbeth seem to be growing apart. Macbeth begins making decisions without her consent or approval. He has Macduff's wife and children killed of his own will. Lady Macbeth begins going down her own road toward insanity. She cannot wash the bloodstains from her hands:
Out, damned spot! Out, I say! One; two; why, then it is
time to do it. Hell is murky! For shame, my lord, for shame! A soldier,
and afeard? What need we fear who knows it, when none can call
our power to account? Yet who would have thought the old man to
have had so much blood in him?
The doctor cannot help Lady Macbeth. She is lost in her own guilt. While she struggles with sanity, Macbeth has gone on his own way, killing whoever gets in the way of his plan. He no longer needs Lady Macbeth for strength. He is stronger than ever it seems. Lady Macbeth has taken a turn for the worse. She is no longer capable of encouragement or influence. Truly, Macbeth has lost Lady Macbeth. She has crossed over into insanity. She is no longer capable of helping Macbeth. The two of them have grown apart.