The 23-year-old was initially charged with threatening to distribute an intimate image of another person, but this was downgraded by prosecutors to using a carriage service to harass someone.
The footballer, who also goes by the surname Trindall, faced Broadmeadows Magistrates Court on Tuesday where full details of the offence were publicly aired for the first time.
In July 2022, Thomas accused his ex-girlfriend of being intimate with another person while they were speaking to each other via Instagram messages, Magistrate Julie Grainger told the court.
The pair began arguing, exchanging a number of messages, and the woman said something about Thomas' mother which he took offence to.
Thomas threatened to share intimate video recordings taken of the two of them and the woman believed he had distributed those clips.
But Thomas did not distribute the videos and has taken full responsibility for his offending in the year since.
His lawyer Sally Vardy said at the time of offending Thomas was not coping with the sudden loss of his maternal grandmother and was dealing with family issues.
"It is a reactive response from Mr Trindall in relation to an immediate message sent by the complainant," she said.
"He received that as a slight against mum and he reacts."
He accepted his behaviour was unacceptable and has taken part in offending programs, social media training and engaged a psychiatrist, Ms Vardy said.
He has also been working part-time cleaning for an Aboriginal start-up business and has returned to playing for North Melbourne football club.
Ms Grainger said the Instagram messages were "harassing, inappropriate, unacceptable" but acknowledged Thomas had taken responsibility for it.
"All of the great work Mr Trindall has done in the last 12 months is for him to learn better ways to deal with conflict, heartache and disappointment, breakdowns of relationships, manage his own emotions, so that in the future he won't respond in such a manner," she said.
She agreed to grant Thomas a diversion, which means he will escape a criminal conviction, and he was ordered to pay $1000 to charity.
"You won't have a searchable criminal record, and hopefully this will be your last appearance in court," Ms Grainger said.
His charge will be withdrawn upon payment to the court fund, which must be made by August 15.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
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