Lucy McHugh bled to death after being left with catastrophic knife wounds in woodland nearly two miles away from her Southampton home in July last year.
Stephen Nicholson, 25, is accused of knifing Lucy in the neck and upper body before leaving her to die after she warned she had a “hold on him” because of their illicit relationship.
He denies three charges of rape against Lucy when she was 12 and two charges of sexual activity with a child when she was aged 13.
Nicholson also denies sexual activity with a 14-year-old girl five years before he allegedly murdered Lucy.
He had been living with with the family when he “exploited” vulnerable Lucy and began a secret sexual relationship in May 2017 with her when she was 12 and he was 23, at Winchester Crown Court heard.
The carer, who also worked as a tattooist, told cops Lucy had messaged him the night before her death saying she was pregnant, it was said.
He explained to police the teenager had told pals she was pregnant, but she later said that she had been referring to her mother being pregnant, the court heard.
Jurors heard she kept detailed diaries about their sex life – writing it had become “increasingly violent” with Nicholson grabbing her neck.
A few days before the teen’s death, Nicholson told a pal she was trying to get him thrown out of the family home in Southampton where he had been lodging for a year, it was said.
William Mousley QC, prosecuting, said the pair had a “big argument”, with Lucy shouting at him “this is all your fault” and “I’ve got a hold on you anyway”.
‘SECRET SEXUAL RELATIONSHIP’
Jurors heard Lucy’s family were aware of rows between the teenager and Nicholson – but believed it was because of Lucy’s romantic feelings towards the care worker.
The prosecutor said: “He had a bedroom opposite Lucy’s. It was clear to family members and visitors there were problems between Nicholson and Lucy which led to arguments which were getting worse in the lead up to her death.
“As a response, one or the other would then stay away from the home. To those who witnessed this, they saw the cause being the behaviour of Lucy towards Nicholson.
“She was wanting his attention, as if she had a crush on him. However, as the investigation continued there was another explanation which was kept secret from her family.
“That concerned a sexual relationship which began in May 2017 and continued for more than a year between a 23- or 24-year-old man and a 12- to 13-year-old girl over a period the prosecution say she was vulnerable to that exploitation.”