In act 3, scene 2, Lady Macbeth is beginning to regret that she and her husband murdered Duncan to gain the throne, saying "our desire is got without content." In other words, she means that they have gotten exactly what they wanted, the crown, but are not at ease or content with it: it hasn't brought either of them happiness.
This is a significant change for Lady Macbeth. Before Duncan's death, she was absolutely sure she wanted to be queen and did everything in her power to manipulate her husband into doing the murderous deed. She even called on dark powers to "unsex" her and kill her compassion so that she could goad her husband into killing his king.
Now, she is filled with a sense of hopelessness because their situation is so unhappy and insecure. She is beginning to think it might be better to be dead, saying
'Tis safer to be that which we destroy
Than by destruction dwell in doubtful joy
In other words, she is doing an about-face. She is realizing the price of destruction (murder) that Macbeth had tried to explain to her before he killed Duncan: it means neither she nor Macbeth can ever again have real joy or peace. She is starting to understand that it is not worth it to be queen under these conditions.
Lady Macbeth and Macbeth, once so close, now try to hide from each other the depth of their unhappiness, though Macbeth's pain is so apparent that Lady Macbeth tells him to appear cheerful at the night's banquet. Macbeth hints to her that he is going to have Banquo killed, but no longer is confiding in her. The two are growing further and further apart, neither wanting to admit to the other what they both know to be true: that the murder was a mistake, and they both are miserable.