Oscar Pistorius shook in court as private text messages from Reeva Steenkamp to him were read out, in which she wrote, "I'm scared of you".
Steenkamp's texts mentioned Pistorius's "jealous tantrums", and accused the disabled star of "picking" on her and being "nasty" to her.
The model, who was 29 when she died, said their relationship was full of "double standards" and said: "I'm scared of you sometimes and how you snap at me."
Following a row at her friend's engagement party, Steenkamp said: "I was not flirting with anyone today. I am terribly disappointed how the day ended."
In another lengthy and candid message sent on the popular message application, WhatsApp, Steenkamp hinted she felt let down by the runner.
She told him: "I cant be attacked by outsiders for dating you and be attacked by you the one person I deserve protection from."
The text messages were read out at North Gauteng High Court during evidence from police captain Moller. The messages were from devices seized from Pistorius's home in the aftermath of Steenkamp's death on Valentine's Day last year.
The devices included two iPhones, two Blackberry phones and two iPads.
In another text messages, Pistorius apparently reveals he asked pal Darren Fresco to take the blame for shooting a gun inside a busy restaurant, only weeks before he killed Steenkamp.
Pistorius, 27, said: "Angel please don't say a thing to anyone, Darren told everyone it was his fault ... I can't afford for that to come out. The guys promised not to say a thing."
Pistorius denies murder and claims he thought Steenkamp was an intruder inside his luxury home on the outskirts of Pretoria. The prosecution alleges he killed her following an argument between the pair.
The trial continues.