Cox was remanded on bail until May 10 for sentencing.
Judge Matenga said that Cox was a "controlling man" who sought to manage all aspects of his victim's life while they were living at the motel.
"She was forced to remain indoors. She was not allowed to smoke outside. Mr Cox insisted that she remain within his sight, even while she was going to the toilet," the judge said.
Cox pleaded guilty at an earlier hearing to misuse of a telephone device after sending hundreds of abusive and sexually explicit texts to his victim over two weeks between March 30 and April 15, 2021.
The court heard from the victim that she received 350 texts from him in one night. He accused her of cheating on him and repeatedly demanded to inspect her intimately.
Cox also sent messages to the woman's son and a friend of hers. He sent all three people pornographic images which he claimed depicted her, and threatened to share them with other people.
One of the assault charges related to an incident in the Napier motel where the two were living on March 30, 2021, in which Cox pushed the woman down onto the bed and placed her in a painful leg-lock.
She said that he also punched her on the chin. Cox had claimed that the contact had been accidental when he was defending himself from the woman.
The second assault charge was laid after Cox threw a piece of garden furniture at the woman after she escaped from the motel unit.
The intimidation charge arose from an incident outside the Latham St Superette in Napier on April 10, 2021, when the woman locked herself in her car as Cox came up to her, yelling abuse, holding up his fist and saying "Do I have to strangle you?" repeatedly.
He later confronted her in the shop but left when another woman intervened.
