Relationships can be fleeting, temporary affairs or they can be lasting associations which benefit all parties.
In Macbeth, we have a variety of relationships between the protagonists and many other characters. At first, we are introduced to the relationship between Banquo and Macbeth. There clearly exists a strong bond between the two - not only are they related in blood and kin, but they are also brothers in arms, comrades and close friends. They seem to trust one another implicitly. The play illustrates, however, how this close bond can be broken when one member is completely overwhelmed by greed or ambition and forsakes friendship to satisfy his lust. Macbeth turns against Banquo and has him murdered. Clearly a very dramatic situation.
To add further drama, we learn about Macbeth's tenuous relationship with the three witches. It is their misguided prophecies which strengthen Macbeth's resolve to commit the ultimate crime, murder. It is Macbeth's relationship with the witches that adds to the dramatic tension in the play.
Furthermore, Macbeth's relationship with his king, Duncan, is at first presented as one of trust, loyalty, honour and respect. However, when Macbeth finally decides to assassinate Duncan, his ambition overrides all these noble qualities evident in his association with Duncan. Macbeth at one point even questions whether his aspirations are enough reason to kill Duncan, given that they have such a good relationship. This further heightens the tension and drama in the play.
There is also Macbeth's relationship with his wife. She is the one who eventually drives him to commit the most foul act of murder when he was in doubt. Macbeth might not have gone through with Duncan's murder if she had not convinced him to do so.
This is how Shakespeare has created an excellent drama by portraying these characters and their relationships.