Brutus cared about Rome arguably more than any other Roman. Love for Rome, particularly the Republic of Rome, coursed through his very veins. A little Roman history is necessary to understand this point.
Brutus came from an old and distinguished family. His great ancestor, by the same name, expelled the last king of Rome and started the Republic. When Sextus Tarquinius raped a Roman matron named Lucretia, Collatinus (Lucretia's husband) and Brutus came together to drive out Sextus Tarquinius's father, Tarquinius Superbus—the king of Rome. They could not stand for the arrogance of Tarquinius Superbus and his evil ways. By successfully banishing him and his family, they established the Republic, which started in 509 BCE. So, by the time of Caesar, the Republic had been going strong for nearly five hundred years.
Based on this history, if anyone loved the Republic, it was Brutus. More than this, the Romans were also very attached to their ancestors. So, Brutus undoubtedly heard the story of his great ancestor all throughout his youth. This point, too, made him zealous for Rome.
Even when he killed Caesar with the conspirators, his love for Rome was on display. Shakespeare probably said it best when he put these words into Brutus's mouth: “Not that I loved Caesar less, but I loved Rome more.”