The so-called "Modimolle monster" Johan Kotze tearfully read out a note to the High Court in Pretoria on Tuesday describing how his now ex-wife ruined his life.
"Ina [Bonnette] ruined my life. I am finished, finished, finished," he read, all the while crying and wiping his eyes.
He is accused of assaulting Bonnette, killing her son, and forcing his workers to gang-rape her.
Kotze said he recognised his handwriting, but did not remember writing the note.
"I must have written it when I got back home."
He testified that he threw his daughter's kitten from his bed the night he saw his wife with another man.
"I did something I never do.... I very aggressively threw [the kitten] away from me."
Kotze testified that he saw Bonnette with another man at a dance on New Year's Eve in 2011.
"I was terribly upset. I froze," he said, taking long pauses and looking at his feet.
Judge Bert Bam asked Kotze if he needed to take a break but he declined.
Kotze said he saw Bonnette hugging and kissing a man with whom she left the dance hall. He followed them.
"It was clear they wanted a relatively dark place where they could be their normal selves. I don't know what went through my head. I was probably powerless."
He said he later left and went to his house, then went to Bonnette's house.
He described watching them being affectionate with each other.
"He lifted up her shirt and I saw his hands on her breasts."
Kotze said he waited and watched them until Ina, the man, and their children left the house again. He went home afterwards.
"It was one of my most difficult nights. I didn't sleep."
A friend told him to end the relationship. He tried to trace the man's car licence plate number.
Kotze said he phoned Bonnette on January 1, 2012. She told him she had not got home late, and had fallen asleep in front of the television.
He said he saw her in town that day and said they needed to talk about what happened on New Year's Eve.
Bonnette attended court proceedings on Tuesday morning. She often shook her head during Kotze's testimony.
Earlier, Kotze told the court he and Bonnette respected each other.
"It was a happy marriage. The problems we had came from outside."
Kotze wore a beige jacket and jeans. He often took off his glasses and rubbed his eyes. His lawyer Piet Greyling asked the court if he could have some water.
"We had respect for each other," Kotze testified.
However, he said they broke up several times before getting back together again.
He obtained a protection order against Bonnette after their second break-up, but went back to Modimolle on November 19 to try to reconcile.
The couple discussed the possibility of renting a house together, he said. He rented the house on his own in Modimolle.
"We decided to see each other in secret. To keep the relationship from her parents for the time being.... Our focus was Christmas and New Year, when it is family time. Then she would reintroduce me to her family."
Kotze, Andries Sithole, Pieta Mohlane, and Frans Mphaka are accused of murdering Kotze's 19-year-old stepson Conrad Bonnette at Kotze's house in Modimolle on January 3.
They are also accused of kidnapping, assaulting, repeatedly raping, and attempting to murder Bonnette that day.
A plea of not guilty was noted on Kotze's behalf after he refused to enter a plea, and claimed his accountability and ability to follow and contribute to court proceedings were in question.
His three co-accused all pleaded not guilty to the charges. They claimed Kotze forced them to take part in the attack on Bonnette and said they had only pretended to rape her.
Bonnette testified Kotze tortured her with various objects before instructing the other three to rape her.
She told the court she listened to her son pleading for his life before he was shot in the head and heart.