I've come to the conclusion that I do not understand Jake Barnes at all. He loves Brett more than anyone else, and for that reason he always overlooks her faults and flaws. Each time she hurts him or makes him jealous with another man, he simply ignores the matter and almost seems to pretend it hasn't happened at all.
I don't understand Brett any better either than I understand Jake though. She too said that she loved Jake in the beginning of the novel, but she is never capable of showing it. Instead, she entertains the affections of all kinds of other men and doesn't remain faithful to anyone. She is most assuredly a promiscuous character who only looks out for herself. Currently, she has decided that she is falling in love with the famous bull fighter, Pedro Romero. I believe that this is largely because of his good looks and great talent as a bull fighter. Mere infatuation, if you ask me. If it were not for his possession of these likeable qualities, she would not be nearly as interested.
"I'm a goner. I'm mad about the Romero boy. I'm in love with him, I think."[Brett]
"I wouldn't be if I were you." [Jake]
"I can't help it. I'm a goner. It's tearing me all up inside." (page 187)
At the end of the chapter, Jake discovered that she and Pedro had the left the cafe alone together. I feel sympathy for Jake in this situation. It must be terribly difficult for him to watch the woman he loves supposedly fall in love with someone else.