Honesty versus secrecy
This novel focuses an incredible amount of its time revealing secrets. Aura and Antonio share secret knowledge about their "relationship"—namely that they only had sex because Aura offered it to Antonio for a better grade in class.
Then he makes friends and learns the friend's secrets. The friend gets a secret message and then is executed—Antonio nearly dies in the gang incident. Then we meet Maya who serves Antonio by telling him more of Ricardo's secrets. The theme of honesty and secrecy is important because it paints a portrait of Colombia that is unimaginably paranoid.
Love, sex, and marriage
One idea that is seemingly absent from the novel is that young single people should fall in love and make families together. That idea is not in the book whatsoever—even though Aura desperately needs the help to raise their child.
The fact that Antonio has a child in this book and doesn't really care about it—that is thematic. The theme here is that Antonio feels so unnerved by drive-by shootings and cartel secrets and drug operations—family is so far out of the question that he simply fails in those roles.
Societal brokenness
Ultimately, what the novel points at is the brokenness of Colombia because of the powerful drug cartels there. Instead of justice by trial, instead of fair punishment, the cartels do business the Wild Western way. They take vengeance all the time against anyone who crosses them. They enforce their reign by literally murdering people in the street.
Therefore the society is broken and paranoid. Although it would be easy to judge Antonio, the reader has an opportunity to use Antonio's own failure as a picture of what exactly it is that he's up against—he could literally be murdered by the cartel just for hanging out with a person they don't like.
