what is tom and daisys relationship like in the great gatsby?

Tom seems pompous and almost displays Daisy as a sort of trophy wife.  Daisy is so focused on being part of the upper class that she appears shallow and focused on her own pleasure.  Their relationship, at some level, seems flawed because he has a mistress and she has little concern about becoming involved with Gatsby when she does.  Still, when she does not go with Gatsby near the end of the novel, the reader hears that there are things about their relationship that no one else can understand.