What is the relationship between Nick and Jordan? How does it reflect on Daisy and Gatsby?

At the end of the novel their connection is nan-existent. Daisy and Tom move away with no forwarding address, and Nick and Jordan break up after she claims to be engaged to another man. Tom and Nick accidently bump into each other in New York, Nick initially refuses to shake Tom’s hand but eventually accepts. Tom admits that he was the one who told Wilson that Gatsby owned the car that killed Myrtle, tells Nick how hard it was to give up the apartment he kept in the city for his affair. He also says that Gatsby's death was well deserved. Nick's conclusion about the couple is that they are nothing but selfish and uncaring people, who live behind the protection their money affords them.

I'm not sure what you mean about how the relationship of the two couples related to Daisy and Gatsby.