Samantha Taylor broke down in court while giving evidence of the trial of her former boyfriend Oscar Pistorius for killing Reeva Steenkamp.
Taylor was comforted by a female friend who went to the witness stand.
Taylor began crying when she recounted how she and Pistorius had broken up for the first time after she claimed the Bladerunner started seeing Steenkamp, a model, behind her back.
Taylor told the court: "He cheated on me," under questioning from prosecutor Gerrie Nel.
Pistorius's lawyer Barry Roux defended his client by claiming Taylor was making up the claim. He said: "I will make emails of emails between you to show that it is not so."
She said they had split up twice. "I was upset." The court adjourned while Taylor regained composure.
Pistorius also appeared to get emotional during the cross-examination as Taylor. He at first appeared to be wearing a look of derision which turned in to sadness, said observers inside North Gauteng High Court.
Taylor said Pistorius had a bad temper and had frequently shouted at her and her relations. She said: "The was a lot of commotion in our relationship. We were still together but we were having problems."
She said Pistorius "would scream out of anger," but not when he was scared. She said he had screamed on "more than one occasion, at me, my sister, my best friend, his best friend."
Tayor was questioned about an incident when a bullet was fired through the sunroof of a vehicle while she and Pistorius were inside. She said Pistorius was "laughing" about it. Also in the vehicle was Darren Fresco, who was the man who passed Pistorius the gun which he accidently fired in a Johannesburg restaurant.
The court also heard about when Pistorius got angry with a police officer after being pulled over just before it happened. Taylor said the disabled runner had shouted at the officer and said he was not allowed to touch the weapon. The shot was fired shortly afterwards.
Taylor told the court; "The shot was fired because they were angry with the police. And they found it funny to irritate the police. I think out of spite after being stopped, it was towards the police."