Reeva Steenkamp was sent hate email for dating Oscar Pistorius and suspected one of his former girlfriends was trolling her on Twitter over their relationship, the runner revealed.
The 29-year-old model told Pistorius in text messages about the dark side of dating him which came from the public attention. She called it "sick" and said people were trying to fill her mind with "doubts".
Steenkamp thought Pistorius's last partner Samantha Taylor was sending her offensive messages via a string of anonymous accounts on the social network, Twitter.
In a WhatsApp message, she told him: "Dating you comes with sick people trying to fill my head with doubts. I learning what's safe."
Pistorius, 27, revealed intimate details of his relationship with Steenkamp, 29, during a second day of cross-examination at his murder trial for shooting her dead. The runner, accused of murder, remained composed during questioning by his lawyer Barry Roux.
He said he had been "besotted" with the model and the pair and purchased plane tickets to Brazil shortly before he killed her.
With Steenkamp's family watching on in court, Pistorius said: "She received a lot of hate mail because of her dating me.
"For Reeva it was very difficult," he said. "At the time Reeva asked Darren [Fresco] to help her because she [Taylor] was attacking her and setting up fake accounts on Twitter to attack her.
"My approach was just to ignore it and don't worry about it. But she [Steenkamp] really struggled with it and I don't think she'd coped with that level of attention that came from dating me. It put a lot of stress on her."
Pistorius and Steenkamp started dating in November 2012 soon after Pistorius cut ties with Taylor after she allegedly slept with another man while he had been competing at the London Olympics.
Pistorius said: "Taylor wrote me an email in which she said some things. She confessed to sleeping with a guy she was seeing while I was at the Olympics, so I never spoke with her again. She got in touch every day but I never replied to her calls, messages or emails."
Pistorius's image was not shown on video cameras inside the court room and only his voice was broadcast.
The runner denies murder and claims he mistook Steenkamp for an intruder inside his luxury home on the outskirts of Pretoria. The prosecution alleges he killed her following an argument between the couple.
The trial continues.