Brian Flynn, of Lanmore Liscarney, Westport, Co Mayo, carried out the harassment against his teenage victim between November 2011 and August 2012.
Yesterday, at Westport Children's Court, judge Mary Devins commended the young victim for being able to cope with such prolonged abuse.
"It is all credit to your son that he didn't take the way out that some other youngsters have done recently and it's also a credit to you as parents," she said.
Over the course of 10 months, the teenager received up to 500 text messages of a abusive, threatening or sexually explicit nature.
The messages repeatedly referred to the teen as 'gay boy' called him a "f***ing bitch" and warned that a group of people would "teach you a lesson".
Text messages were also sent to locals in the Westport area claiming to be from the young victim and signed off by him. As a result of these texts the teenager was assaulted by a number of people.
The court heard that Mr Flynn had taken up his campaign against his young victim for no apparent reason. He yesterday apologised in court to his victim and the teenager's family.
"I just can't apologise enough. It will be with me for the rest of my life. I know I've caused so much trouble to someone so young and it tears me up to know I've done it and I'll never be able to put it right," he said.
As a result of the abuse, the teenager's parents took his phone in December 2011 and alerted gardai. The messages were then monitored. Gardai enlisted the help of the Crime and Security branch and Vodafone Ireland in a bid to trace the culprit.
They were able to monitor when the phone was topped up and Sgt Pat Lavelle of Westport Garda Station then downloaded CCTV footage of Mr Flynn buying the top-ups from local service stations.
When he arrested Mr Flynn on August 24 of this year at the shop where he worked, Sgt Lavelle noticed Mr Flynn drop his mobile phone behind the counter. It was retrieved and found to be the phone that all messages had been sent from. Mr Flynn was charged with harassment and admitted to the charge.
"He didn't give any explanation as to why he'd done this," added Sgt Lavelle.
"It was my own problems that I let build up over the years that had all come to a head and I was looking for a distraction I suppose," said Mr Flynn.
Judge Devins adjourned sentencing until next February.