Louella Fletcher-Michie, 24, overdosed and died as her boyfriend, Ceon Broughton, 29, filmed her after giving her the drugs, it is alleged.
She took the Class A party drug 2-CP at Bestival, in Dorset, on September 10 2017 and died an hour before her 25th birthday.
Her parents rushed to the site after telephoning Broughton as Louella overdosed and heard her “screeching”, Winchester Crown Court heard.
However, Broughton insisted she was fine and referred to Louella as a “drama queen”, jurors heard.
Broughton, of Enfield, north London, denies manslaughter and supplying Louella the drug.
Prosecutor William Mousley QC said Broughton failed to get help because of a suspended jail term he was handed one month earlier and feared the consequences, the court heard.
He said: “She died as a result of having taken a large dose of, later described by the defendant as an overdose, of a Class A drug known colloquially as 2-CP, which he had given her at a music festival.”
Mr Mousley added: “It had a terrible effect upon her, leading to her death after a significant period of suffering in woods close to the festival site, all of which he must have observed.”
Jurors were told Broughton filmed Louella, a dancer and yoga teacher, as her condition deteriorated.
In clips shown to the court, she repeatedly shouts at Broughton to telephone her mother, Carol Fletcher-Michie, but he tells her to “put your phone away”.
Ms Fletcher-Michie eventually spoke to Louella at 6.48pm and grew concerned after she “could hear her screeching”.
Mr Mousley said: “She told her husband that they needed to get to her and they dropped everything to travel from north London to Dorset.”
Her brother, Sam, also contacted Broughton and urged him to seek medical help.
But Broughton sent Sam a message which said “call back in an hour” and referred to Louella as a “drama queen”, the jury heard.
Jurors were told Sam also knew Broughton and had been given drugs by him previously.
Mr Mousley added: “In addition, during that extended period of time when they were together he filmed her on a number of occasions.
“He filmed her when she was disturbed, agitated, and then seriously ill over a period of hours.
“He even did so, the prosecution suggest, after she was apparently dead.”
He said that a month before the incident, Broughton was handed a 24-week prison sentence suspended for one year.
Mr Mousley said: “His failure to get her treatment which may well have saved her life was borne of selfishness and in self-preservation.
“Because to have done otherwise, to have acted positively, he knew would have exposed him to the possibility of arrest and prosecution for a criminal offence punishable with imprisonment.”
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