Shortly after the couple were dropped at Ruddelle's Manurewa home, they had an argument and she stabbed him twice in the chest using a kitchen knife with a 19cm blade.
The Crown alleged Ruddelle stabbed Ngapera with the intention of killing him or seriously wounding him.
However, the defence says that after years of domestic abuse she "knew what was coming" and used the knife to protect herself and her 14-year-old son.
Ruddelle's lawyer Shane Cassidy told the jury that the teen had woken to hear his mother screaming for help and intervened in the altercation - putting himself between her and
Ngapera.
Her actions were in defence of herself and her child, the defence says.
The trial before Justice Matthew Palmer and a jury is set down for two weeks.
Crown witnesses include family members of both Ngapera and Ruddelle, neighbours, police and staff who were working at the bar the couple were drinking at before the alleged murder.
The first witness called by the Crown was Ngapera's cousin Charlotte Howard.
She said she was "like a sister" to Ngapera.
He spent about 20 years living in Australia and returned to New Zealand, where he spent time living on the streets and with Howard.
He then met Ruddelle and moved in with her.
Howard said her cousin introduced his new partner to her and, from what she could see, the pair got on "good".
The couple often spent time at Howard's place.
"What I observed is they were good when they were drinking together," Howard said.
"[They would be] laughing and joking together."
However, after drinking alcohol, the pair would "argue".
"I'd tell them to stop it, to cut it out," said Howard.
She said the arguments came after Ngapera wanted to purchase more alcohol but "Karen said no".
Ngapera would then say "pretty rude" and "unforgivable" things to Ruddelle.
"He used to swear at her ... all the unforgivable names," she stated.
She was reluctant to repeat the names but said one was "black b**ch".
"She didn't like it, she used to try and calm him down ... she'll just walk out," Howard recalled.
"She told him to grow up, stop drinking, she said that a lot."
Howard said she never heard Ruddelle return insults to Ngapera, but she did refer to him as "a drunk".
"I told him to cut it out, leave her alone," she said.
Ngapera left Ruddelle's house a number of times and Howard said he told her it was because she was "taking his benefit" and "using it to feed her family".
Howard told the jury that the last time she saw Ngapera before he died, he told her that he'd had a fight with Ruddelle at the pub.
"He told me she was flaunting herself around at the pub and he was getting angry at that," she said.
"She rang him up, they had a few words ... he was calling her a slut ... ungodly words ... he was pretty loud.
"She told him to quieten down, talk properly to her ... he started being good to her again.
"He turned around and said 'cuz, I'm leaving now, Karen's alright with me'."
A week after that conversation, Howard said her cousin was dead.
Ruddelle's lawyer Shane Cassidy questioned Howard about Ngapera.
She confirmed that he had stayed with her when he was charged with breaching a protection order that the courts had granted in favour of Ruddelle.
Howard described one fight that ended in Ngapera "chasing" Ruddelle in a car.
She said he was "trying to run her down".
Howard said despite the issues the couple had, they had strong feelings for each other.
"He loved Karen," she said, becoming emotional.
"She did love him ..."
Ngapera's sister Ngaire also gave evidence.
She said when he was about 24 he was in a relationship with a woman named Olivia Abraham.
She witnessed her brother being violent towards her.
"He gave her a slap across the ears because she took the car without [telling] him," she revealed.
Ngaire Ngapera said she did not see her brother being violent to any of his other girlfriends.
The trial continues.
DO YOU NEED HELP?
If you're in danger now:
• Phone the police on 111 or ask neighbours of friends to ring for you.
• Run outside and head for where there are other people.
• Scream for help so that your neighbours can hear you.
• Take the children with you.
• Don't stop to get anything else.
• If you are being abused, remember it's not your fault. Violence is never okay.
Where to go for help or more information:
• Shine, free national helpline 9am- 11pm every day - 0508 744 633 www.2shine.org.nz
• Women's Refuge: Free national crisis line operates 24/7 - 0800 refuge or 0800 733 843 www.womensrefuge.org.nz
• Shakti: Providing specialist cultural services for African, Asian and Middle Eastern women and their children. Crisis line 24/7 0800 742 584
• It's Not Ok: Information line 0800 456 450 www.areyouok.org.nz
