Lord and Lady Macbeth have a very complicated and changing relationship. It is clear from the beginning of the play that they do genuinely love and care for one another. Macbeth takes time to notify Lady Macbeth of the witches prophecies. They plan the murder of Duncan together. However, in the beginning of the play Lady Macbeth seems to be the dominant member of the relationship. She feels that Macbeth is too soft to do what needs to be done. She mocks him, telling him that he is not manly enough and that she is more of a man than he is. She follows through with framing the soldiers when Macbeth can't. Macbeth is the first to show signs of guilt, seeing the ghost of Banquo, and Lady Macbeth covers for him. After Macbeth plots against Banquo on his own though, their relationship changes. Macbeth feels impowered and untouchable after the apparitions. Lady Macbeth warns him that he is shedding too much blood and he ignores her. Lady Macbeth goes insane with guilt, and the only sympathy Macbeth gives her is that if she had died on a different day he would be able to properly mourn for her. Both are ambitious, and their ambition changes their relationship and turns them away from each other.
I have always felt that the relationship between Lord and Lady Macbeth was certainly an interesting one of the time. This is because although Lord Macbeth is certainly doing his manly duties by fighting in bloody wars, Lady Macbeth seems to rule the roost mentally. For example, when the witches suggest the opportunity for Macbeth to foster his "vaulting ambition" by killing King Duncan, Macbeth runs immediately to write his wife to see what she thinks about the whole thing.
Whiles I stood rapt in the wonder of it, came missives from the King, who all-hailed me "Thane of Cawdor," by which title, before, these weird sisters saluted me, and referred me to the coming on of time, with "Hail, King that shalt be!" This have I thought good to deliver thee, my dearest partner of greatness, that thou mightst not lose the dues of rejoicing, by being ignorant of what greatness is promised thee. Lay it to thy heart, and farewell. (1.5.6-14)
In other words, the magnanimous decison would not be made withought his wife's thoughts embedded in the mix: very odd for an English male of the time! To take this idea a little bit further, let's consider what happens next. Macbeth waffles in his decision so much and is incredibly unnerved by it (even to the point of hallucinating); therefore, Lady Macbeth takes it upon herself to make the decision for him. The irony here is that the actual decision (to kill Duncan), after carried out, is the death of Lady Macbeth, . . . while Lord Macbeth lives long enough to allow his own "vaulting ambition" to be his tragic downfall.