Janbaz Tarin admitted fatally stabbing Raneem Oudeh, 22, and her 49-year-old mother Khaola Saleem outside their home in Solihull on 27 August.
Ms. Oudeh had dumped her husband in the weeks before the attack after discovering he had three children and a secret wife who was pregnant with a fourth child in Afghanistan.
She learned of his other family six months into the marriage, which was carried out under Islamic law, and tried to leave him before he became violent towards her.
In the weeks before her murder, Ms Oudeh told family members he had threatened her, saying “if you leave me, I will kill you and your family”. She had been living with him and her two-year-old son but neighbours said she had moved back to her mother’s home weeks before she was killed after a number of rows that had led to the police being called on several occasions.
But Tarin repeatedly harassed his ex-partner, sleeping outside Mrs Saleem’s address for 12 consecutive nights.
An investigation into the police response is being carried out by the Independent Office for Police Conduct.
On the night of the murder in August, the pair were seen on CCTV arguing at a shisha lounge in Birmingham. Ms Oudeh, who was with her mother as the argument escalated, was seen calling 999.
Tarin’s white van was then captured driving towards the family’s home in Solihull where he waited for their return and stabbed them both to death.
Inside the house, Ms Saleem’s husband of 16 years, Mohamed Saleem, heard the screams of his wife and stepdaughter and ran out to try to help them.
“It’s indescribable, it’s a nightmare, it’s heartbreaking,” he told Sky News.
“Two loved ones gone on one night and we’re all wondering why. What was the need to take the lives of two beautiful personalities?”
Ms Saleem’s mother, Salima Hobee, helped to bring up her granddaughter. She described her heartbreak when Ms Oudeh’s son asked where his mother was and they had to tell him she had gone.
It later emerged that Ms Oudeh had made a number of panicked calls to the police in the hours before her death and was on the phone to officers as she was fatally stabbed.
Her aunt Nour Norris, who now takes care of her young son, believes the double murder could have been prevented.
“Raneem was known to the authorities months and months before the murder happened as being in a violent relationship,” she told Sky News.
“We want to know why they were let down by the authorities, why they were let down by everybody that night. And [only then] we’ll make sure that doesn’t happen to other vulnerable women.”
Detective Chief Superintendent Mark Payne from West Midlands Police said: “My assessment based on events of the night is that it unfolded very very quickly.
“We did respond to the calls that came in and went to the locations where they were but they’d already moved on from those locations so I think we did our absolute best.”