The man - referred to as Mr X - stole "embarrassing" photographs of his former partner and threatened to publicise details of her new relationship by using the pictures as well as a number of stolen notes and letters, said Graham Blower, for the prosecution.
"He became bitter and twisted and decided to get money off her for all he believed he had done for her in the past, although in law he knew he had no right or claim against her."
Mr X, who is in his fifties and was originally from the Midlands, denies conspiracy to blackmail.
Mr Blower said that the middle-aged woman, Mrs A, had lived with Mr X for a number of years. He had given her financial assistance and gifts, and was, in the early stages of the relationship, a man of considerable means.
She also gave him help, although it was not necessarily financial, Mr Blower added. For instance, when he was involved in an accident, she looked after him. But the relationship went sour and Mrs A started a relationship with another man, referred to as Mr B.
By this time, Mr X was struggling financially and saw his situation as being the fault of everyone but himself, according to the prosecution.
Mr Blower said that Mr B had a high-powered job and gave Mrs A pounds 50,000 as a gift, together with a note, and that the note was later used by Mr X, or a second man acting as an agent, to blackmail the couple.
Personal items, including keepsakes and postcards showing the nature of the relationship, were stolen from Mrs A after a screw was removed from a window to gain entry to her home.
The couple also received a number of calls at their homes and workplaces.
"The tone was that unless they paid a sum of money, items stolen from them - photos of her on holiday, embarrassing photos to her and her reputation - would be released to the Sunday papers," Mr Blower said.
"Much play was made about what would happen to their reputations. You may think this would cause anyone to think they were being blackmailed," he told the jury.
Mrs A was told that she could buy the items back for pounds 8,000, he alleged.
The court was told that Mr B was also sent a fax entitled "The Infernal Triangle", which complained of Mr B's behaviour.
He was also allegedly rung at work by a man saying he had evidence that Mr B used prostitutes. The caller ended by saying: "I have every intention of exploiting it."
A meeting was arranged at a McDonald's restaurant in London. But by now the price being demanded for the return of the stolen property had dropped to pounds 3,000, the jury was told. Police had been alerted, and Mr X and a second man were arrested.
Mr Blower said that the second man had admitted being involved in blackmailing the couple.
He went on: "What it comes down to is, was he doing it on his own or was he working as an agent for Mr X? Requests of money may have been made, but did it go as far as blackmail?"
Mrs A told the court that Mr X had said he wanted money from her and that he was going to embarrass her.
In April 1997 she received a call at work from a man she did not know, who said: "We have some material - the Sunday papers are very interested." The man said it was a topless photograph, she said.
"I received phone calls the whole day - increasingly threatening. I was in a very shocked state.
"All the items sent to me by Mr B should have been in a cupboard in my house. I checked the cupboard and realised that not only were some items missing, but that they had been sifted through and things carefully removed which might seem salacious."
Mr Blower said: "It was the breakdown of a relationship, and Mr X embarked on a course to get money out of her or, if not her, a man with whom she had started a relationship and who he blamed."Reuse content