Samantha Taylor also testified that Pistorius had cheated on her twice and their relationship ended when he cheated with Reeva Steenkamp, whom Pistorius is accused of deliberately shooting to death Feb. 14, 2013, the BBC reported.
Pistorius, the double-amputee Paralympian, denies deliberately killing Steenkamp, saying he thought he was shooting at an intruder behind a closed bathroom door in his Pretoria home.
Pistorius' attorneys pointed to emails they said demonstrated their client's relationship with Taylor had ended by the time he began dating Steenkamp, while Taylor said the relationship was not "officially" over.
Taylor also testified the alleged shooting incident -- which Pistorius also denied -- occurred when he became angry after a police officer stopped him for speeding, saw the gun and told him it couldn't be left on the car seat. She said he fired the gun through the vehicle's sun roof.
The trial recessed twice when Taylor broke down and cried while on the stand, the BBC said.
Also Friday, Pieter Baba, a security guard on duty the night of Steenkamp's death, testified about what he saw and heard from neighbors and in Pistorius' house after the gunshots were fired, Britain's the Guardian reported.
Baba testified that Pistorius told him "everything is fine" after neighbors reported hearing gunshots fired from Pistorius' house.
The trial adjourned until Monday.