The main issue that Nick discovers in the marrige of Tom and Daisy is that neither one truly loves the other. Tom doesn't love Daisy and views her as arm candy, and he uses her as a social boost. His lack of love is evident as Nick soon finds that Tom has an affair with Myrtle, a woman residing in the "valley of ashes." Daisy is at fault too for this loveless marrige. Daisy sees marrige with Tom in a series of three points. Firstly, she marries Tom for economic stablility because he is extremely wealthy. Secondly, Tom represents a path to the top of the elite social class, and Daisy happily makes the trek down this path. Lastly, Daisy marries Tom because it is the morally right thing to do in the time period, since she had committed to do so even though she was in love with Gatsby. This marrige was doomed from the start, and the two could be seen as "star-crossed lovers"--with out the "love," of course.
Nick learns that Tom and Daisy's relationship has some problems, namely that Tom is having an affair with another woman. Nick becomes aware of this when the telephone rings for Tom during dinner. After Daisy goes to talk with Tom, Jordan tells him that this woman is Myrtle Wilson, who lives in the "valley of ashes". This scene of but one of the many scenes where Nick realizes how corrupt and terrible the upperclasses can be.