What causes the breach in Octavius and Antonius' friendship?

Octavius begins speaking to small groups of people, wondering aloud at the fact that the murderers have not yet been punished, followed by a public announcement that he will pay the monies to the public meant to be paid by Antonius. In response, Antonius immediately introduces legislation to prevent the adoption of Octavius into Caesar’s family and makes open threats on his life. Eventually, Octavius and Antonius reconcile, but they begin quarrelling again not long after; they go back and forth so much that no one knows when they are allied or opposed.