What does Fitzgerald seem to be saying about the identity concept at this point in the novel?

From this quote, Myrtle saw her identity in terms of others.... who they were, what they represented.... how they reflected upon her. She says that she married impulsively, which means she merely wanted to be married, the man didn't really matter. She was also appalled that Wilson had to borrow a suit, something that disappointed her because a man without a suit alluded to someone who was successful. The fact he couldn't even afford a suit made her decision a mistake.... the fact he hadn't told her he had to borrow a suit was seen as deceit.