The friend told the court the complainant had become "distant and strange'' in 2017 while in a relationship with the accused.
In November, the women met up just days after the final alleged incident.
Before the meeting, the complainant made her friend "promise not to freak out'' - her face was badly bruised.
The woman said her partner had "punched her in face, yanked by hair and kneed her in ribs'', the witness said.
Another person at the house that day said the complainant was "very swollen and bruised'' and walked with a limp.
They convinced the woman to see a doctor but she was adamant she did not want the police involved.
Her best friend ignored her wishes though and they had not spoken since.
"I lost my best friend through this, when I went to the police and let them know what he was doing,'' she told the court.
The couple said they were going to fix the issue themselves through counselling but that did not convince the friend, who said "It was way too serious.''
The first of three alleged incidents took place in Christchurch when the pair attended a family function. The woman suffered a burst eardrum following what she initially claimed were 50 slaps to the face.
A second episode allegedly involved strangulation to the point where the woman "feared for her life''.
The third happened on a drive home from a boozy barbecue. The defendant allegedly punched the woman as she drove his truck, which resulted in her driving into a hedge and leaving the scene.
Police say the violence continued at the house later but the complainant said the blows were only slaps and "It wasn't a victim-attacker situation.''
The woman, who delayed the trial more than once by failing to show up to court, said she wanted to continue a relationship with her partner.
She sat in the public gallery yesterday to support him.
Judge Michael Crosbie reserved his decision.
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:
• Women's Refuge: Free national crisis line operates 24/7 - 0800 refuge or 0800 733 843 www.womensrefuge.org.nz
• Shine, free national helpline 9am- 11pm every day - 0508 744 633 www.2shine.org.nz
• It's Not Ok: Information line 0800 456 450 www.areyouok.org.nz
• Shakti: Providing specialist cultural services for African, Asian and middle eastern women and their children. Crisis line 24/7 0800 742 584
• Ministry of Justice: www.justice.govt.nz/family-justice/domestic-violence
• National Network of Stopping Violence: www.nnsvs.org.nz
• White Ribbon: Aiming to eliminate men's violence towards women, focusing this year on sexual violence and the issue of consent. www.whiteribbon.org.nz
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