The main way in which Macbeth and Lady Macbeth's relationship changes in Act 3, Scene 2 is:
b. Macbeth becomes more independent and makes decisions on his own.
In this scene, Macbeth starts to take charge and makes decisions without consulting Lady Macbeth, particularly regarding the plans to murder Banquo and Fleance. This marks a shift in their dynamic, with Macbeth asserting more control over his actions and choices.