How do Lady Macbeth and Macbeth drift apart after the murder scene of Macbeth?
Readers don't get much detail as to how Macbeth and Lady Macbeth drift apart in Shakespeare's Macbeth, we just know that they do. We aren't privy to the workings of their minds concerning their relationship (no dialogue or soliloquies on the subject exist). We just see them not working together anymore.
In fact, drifting may not even be a good word to describe the change in their relationship--it seems pretty immediate.
In Act 2.3 after the two collaborate on Duncan's murder in Act 2.1 and Act 2.2, Macbeth veers from the plan devised by his wife and kills the two grooms who sleep outside of Duncan's chamber. This immediately puts him under suspicion (by at least Macduff) since they are the only two likely witnesses, and causes his wife to faint (because it is so stupid).
Macbeth, apparently, then is determined to make his own decisions. Perhaps he resents the way his wife manipulates him before the killing of Duncan, but that is only speculation.
All we know for sure is that the two no longer collaborate, and Macbeth "wears the pants in the family," to his own detriment, for the rest of the play, planning the murders of Banquo and Fleance and Macduff's family all by himself, all of which lead to his downfall.
The murder scene represents a role reversal in the two characters of Macbeth and Lady Macbeth. Until this point in the play, Lady Macbeth has been the driving force. She thinks ambitiously about their political careers while Macbeth thinks more conservatively.
Following the murder scene we see Macbeth take center stage. Murdering Banquo and becoming the bloodthirsty tyrant that drives his Lords to join his enemies. Lady Macbeth, who was so masculine at the beginning of the play, faints after the murder and is driven to madness, presumably because of guilt.
Both characters are too absorbed in their own roles as King and Queen, Tyrant and guilt ridden maiden, to take much interest in each other.
With the passage of time, it would make sense that Lady Macbeth and her husband drift apart after jointly engaging in murder and immortality. Certainly, they are still together in both name and action, but over the arc of the play, Macbeth becomes more dependent on the witches and their prophecies as well as more consumed with greater plunging into moral quagmires, while Lady Macbeth becomes more obsessed with appearances and her distance from her husband is assisted with her own guilt. I think that it makes sense that both would become more distant from one another as the greater immorality results.
Prior to Duncan's murder, Lady Macbeth is in charge and telling Macbeth the plans. He must be persuaded to murder King Duncan. After the killing of Duncan, Macbeth takes control and leaves Lady Macbeth out of the planning of future murders. She tells him to enjoy being King, and he tells her that he cannot. He is too worried about the threats, real and imaginary, of others to be satisfied with what he has achieved.
He hires murderers to kill Banquo and Fleance. He does not even consult her on this plan or inform her of his desires. He tells her to "be innocent of the knowledge, dearest Chuck" and talks to the murderers alone.
Next, he decides to have Macduff's entire family killed and sends murderers to complete this job, as well. Again, he never consults Lady Macbeth or advises her of the plan.
These murders lead to Lady Macbeth losing her mind and sleepwalking because of the guilt. When Macbeth is told of her problem, he just tells the doctor to take care of it.
When Lady Macbeth commits suicide, Macbeth says that he wishes he had the time to mourn her properly, but he is too busy with the problems at hand.
These events indicate how the two drifted apart after Duncan's murder. Macbeth is the one who decided to go on without Lady Macbeth's help and advice.