The 59-year-old former clinical psychologist, who cannot be legally named, is accused of raping and molesting the 15-year-old boy in his office on the NSW north coast in mid-2017.
The teen, who attended the clinic twice, claims that his mother was told to wait outside at the initial session.
The psychologist allegedly said he would watch pornography on his phone while the boy answered a text from his father before suggesting that he could visit a nude beach to relieve stress, jurors at a District Court criminal trial have previously heard.
The boy faced a grilling by defence barrister Anita Betts on Thursday where he was accused of lying to police and the court about this alleged conduct.
Ms Betts suggested that the teen had brought up "nudity and going to a beach" to stir up his mother while she filled out forms for the psychologist.
"No, I never said that," he said.
"He was the one that suggested the nudist beach to me."
He denied lying about this, saying he was 15 years old at the time and had no reason to broach the subject.
He also rejected suggestions that the psychologist had not mentioned pornography during the session.
"You are lying. I believe you are lying," he told Ms Betts.
The sexual abuse and rape allegedly occurred at a second session.
The teen did not tell his parents immediately after because he was fearful, jurors heard earlier on Thursday.
"He told me if I told anyone he'd kill me, so I was scared for my life to say a single word about it," he said under questioning by crown prosecutor Steve Wilkinson.
The boy believed the death threat because the psychologist had all his details, keeping the alleged incident secret for years.
He only told his parents and made a statement to police after hearing about the psychologist's arrest.
"I knew something f***ing happened with him," the boy's mother allegedly said after her son revealed the claimed sexual assault.
The complainant told jurors he stopped going to school after seeing the psychologist, withdrawing to his room.
He slept during the day and couldn't sleep properly at night, having nightmares where he relived being raped, he told the jury.
The psychologist has pleaded not guilty to one count of indecent assault and one count of sexual intercourse without consent, both relating to allegations with a boy under 16 years old.
He has denied that anything untoward took place.
Prosecutors have told jurors about claimed admissions by the 59-year-old of separate sexual abuse of a number of other former patients.
These prove he had a tendency to act in a certain way, Mr Wilkinson said on Wednesday.
The psychologist denies this, saying he was coerced or induced into making the admissions by his former lawyers.
The trial continues on Friday.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
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