what was the relationship between cesar and antony

Antony, the heroic leader of the forces that defeat Brutus and the other conspirators, is also the title character in another Shakespearean tragedy, Antony and Cleopatra. In Julius Caesar, Antony is introduced in 1.2 and his importance is indicated by Cassius's proposal that he be assassinated along with Caesar (2.1). Antony delivers his most significant speech (in either tragedy) in 3.2: "Friends, Romans, countrymen, lend me your ears…" (79). After Brutus commits suicide, Antony eulogizes Brutus in a speech that begins with one of Shakespeare's best known lines: "This was the noblest Roman of them all"(5.5.68).

You might also find the essay linked below useful, "An Examination of the Relationship Between Marc Antony and Julius Caesar."