Which best explains why Brutus chooses to commit suicide at Philippi? Caesar's ghost urges him to do it, and Brutus is too afraid of the ghost to disobey it. Cassius betrays Brutus and joins forces with Octavius and Antony. Brutus kills himself because, to ancient Romans, suicide was an honorable way to die if it helped one avoid defeat and humiliation. Antony and Octavius demand that he commit suicide, and Brutus gives in to their demands.