"This action has been as a result of, I think it was when his house was broken into, it was the response to that. He's just lost his cool and has responded in a very poor manner."
Matiu and his partner have been involved in three previous family harm incidents. They have a child together who was not present at the time of offending.
Police prosecutor Graham Hoskin said the offending occurred at about 10.30am on September 6.
"During the day the defendant sent a number of Facebook messages to the victim," Hoskin said.
"They included calling the victim a ****ing bitch and a dirty whore."
Matiu pleaded guilty to a charge of threatening to kill or do grievous bodily harm in Whanganui District Court.
Judge Garry Barkle noted in sentencing Matiu, a self-employed mechanical engineer, that he had not offended for two years.
"I have your previous history and as the sergeant has drawn to my attention, and it is a concern to myself, you've got the four previous protection order breaches in your past," Barkle said.
"I assume that your relationship has broken down and it has ended, but if not then that presents a level of concern and volatility around your whole situation."
Judge Barkle sentenced Matiu to nine months' supervision and 100 hours' community work.