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:

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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:

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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:

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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:

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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.