He lost his nerve. The person he asked to kill him was by the way not a slave, but a freedman - Epaphroditos - who had been his personal secretary for years.

Livia, Octavian/Augustus's wife. He was killled by poisening from... gasp! Livia!

he committed suicide because he killed his sister (which was a horrifying death because he got his sister pregnant when she was going to have the baby he cut her open took out the baby that killed the sister but then he killed the baby by choking her)

Correction. The above answer is confused with a story about the emperor Caligula, not Nero. Nero committed suicide after he realized that the revolt against him could not be stopped. Rather than face the disgrace of being flogged to death, he killed himself.

Nero death was on June 9th 68AD. Nero could not kill him-self, so he had his private secretary to kill him for him. The secretary's name was Epaphroditus. A senate had declared Nero an enemy to the public, so the people would have him beaten to death. The soldiers were coming to kill him coming his way.

Nero died on June 9th, 68 AD, choosing to commit suicide rather than face the decree of the Senate which had sentenced him to be flogged to death because of his atrocities and loss of power over his own armies and allies. Suetonius writes that Nero fled Rome on the Salaria road, stabbing himself with the assistance of his secretary Epaphroditos when the praetorium guard caught up to him. His last words were: "Qualis artifex pereo" which translated reads "What an artist the world loses in me."