In the final chapter, after Gatsby's funer, Nick says he'd had enough of the fast, glittering life in New York and decided to return to the midwest. Nick knew he had to break if off with Jordan and he was tempted to just leave without a word, but that would have been irresponsible. That would have been too much like Tom and Daisy and their self-centered quality and irresponsible nature. He was sick of that very aspect of the people he encountered there in New York. He saw too much of people living for and thinking about only themselves and not about the people they might meet and hurt along the way. It all ties in with the philosophy that Jordan has about how she doesn't bother to watch out for others because she believes they will watch out for her since it takes two to make an accident. Jordan knew, from the phone conversation she and Nick had when Nick set up this last meeting, that Nick was breaking up with her. Still, Nick felt it was his responsibility to meet Jordan face to face to formally break up with her. When Nick left the midwest to come to New York, one of the reasons he left was that people had linked him and another woman to the point where he was afraid that rumor and gossip would have him engaged to the young woman. He left rather than face up to all that innuendo. He's learned a lot about life in his short time in the east and he will not just leave without clearing up everything with Jordan first.