Please elaborate on this idea: Infinitely keener than Lady Macbeth is Macbeth's suffering.

While both Macbeth and Lady Macbeth have minds that become unhinged, Macbeth's actions compound his suffering which is longer-lived than Lady Macbeth's. Lady Macbeth gives way to mental instability relatively early in the tragedy of Macbeth and her symptoms of instability render her obsessed and void of the power to act outside the confines of her obsession. This means that she is limited in the extend of further harm that she can do, either by way of direct action or indirect influence. Her mental disordered state soon leads to her demise.

Macbeth, on the other hand, though he becomes unhinged upon receiving the news that Fleance has escaped has, for all intents and purposes, the appearance of normality and can still act and precipitate events, which he does with a vengeance. Macbeth's unhinged mental condition isn't of the sort to bring relief in death and thus he goes on to add atrocity to atrocity. On top of which, his desperation leads him to turn to those who unleashed the havoc in the first place, the witches, who give him information that he receives as being for his betterment but which really is, as their first sets of prophesies were, only for his destruction. Since woe upon woe and evil deed upon evil deed are heaped on Macbeth's heart like coal in a furnace, Macbeth's suffering is infinitely keener than Lady Macbeth's.