At the end of Chapter 3, what does Nick tell himself he needs to do before he can fall in love with Jordan Baker?

There is a roughly drawn love affair that remains
unfinished in the midwest. He must first write a letter to break up with her before he
can allow himself to get closer to Jordan. Fitzgerald is making the point that, though
love affairs can be murky in nature, there is a proper way in which to handle
them.