I think Robert Cohn represents the manhood that Jake didn't have. First of all, Cohn is a box champion, and the stereotype of that kind of people is a dumb, strong, virile one, everything of what Jake is not. Another point of this character is that, in the whole book he is trying to enter to the social group and admires Jake, compared to Barnes, he is "glued" to the group, though he is really an outsider.
The title, "the Sun Also Rises" gives a meaning, that everything even the sun must go on, no mater what. Jake's injury and his love for Brett were going to be present in every step of his life interfering and putting obstacles in Jake's wishes; though his life still goes on.
Neither of the characters can control themselves. They act really impulsively, Brett acts like a real slot every time she is able to, no matter whom she is with. Cohn acts childishly. Jake doesn't want to participate in anything that he could be personally involved to. .
The great quantity of alcohol they drank means the way they feel about life. They let it go without worrying how deep and injured you can get, so they drank all day to forget the past, and to give some cheap reason to their every day life an habits.
The fact that Hemingway is a lost generation character, is reflected in the way must of his characters feel. They don't have any future plan, they forget about their families, don't care about the money, or even their jobs; they have no perception of what they really wanted, so all of them were lost.
The bullfighting gives me the idea of a kind of sexual ritual between the bullfighter and the bull, so it means that Brett has sex like an animal, she has had sexual relationships with a lot of bulls, animals, or characters, but there are only two significant characters that really matter to her, Romero and Jake. Romero is a real bullfighter, so he plays his.
natural roll, but the place of Jake in the symbolic bullfighting, is that Jake tries really hard to escape from the bull, Brett, so he cannot be "penetrated" by the bull's horns.
