Caroline Crouch, 20, was smothered to death by her husband Babis Anagnostopoulos, who then staged an elaborate cover-up to make it appear as though she had died in a botched burglary.
In a bid to make his lies look more believable, he also drowned the family's husky puppy.
After eight hours of police interrogation, Anagnostopoulos confessed and said he lied because he did not want their 11-month-old daughter Lydia to grow up without parents.
Ms Crouch's diary entries show how the couple had a fiery and toxic relationship, amna.gr reports.
When pregnant with Lydia in 2019, Caroline wrote: "Last night we fought with Babi because I had a meltdown because of my hormones.
"I yelled at him and hit him and told him I don't want our baby...
"I am not well, I am very upset, I would obviously never hurt my baby," wrote Caroline.
"My love for her is stronger than anything in the world,"she noted, also mentioning that she was ashamed to tell her husband that her hormones were affecting her so strongly.
"I love him so much that I can't leave him even though this relationship hurts me," she wrote.
She continued to detail other arguments in the diary over the coming months, blaming her hormones.
In one diary entry, she wrote: "I fought with Babi again. This time it was severe.
"I hit him, I cursed at him, and he broke down the door.
"All I wanted was for him to ask how I am when I woke up. I woke up so weak and tired.
"I am thinking of leaving. I am thinking of going to my sister, I don't know if I can keep going with Babi."
In July 2020, on their daughter's first-month birthday, Ms Crouch wrote in her diary about how she had told Anagnostopoulos that she wanted to leave and had found a house in Halandri, another Athens suburb.
"Today my little one is a month old- it's also the day I told Babi I want to leave...I feel awful." she wrote.
Ms Crouch, who grew up on the Greek island of Alonnisos was found murdered in a bedroom on May 11 after her husband reported the crime to the police.
Anagnostopoulos, a 33-year-old helicopter pilot and flight instructor, made several statements hours after the killing, telling reporters they had been tied up by robbers who broke into their home in Glyka Nera.
But police revealed on Thursday that this was, in fact, not true, and Anagnostopoulos had confessed to killing his wife.
The Greek helicopter pilot had been charged with the murder of his British wife after claiming she was killed during a robbery at their home outside of Athens.
He admitted suffocating her during a fight at their home in the early hours of May 11.
In the pilot's grovelling admission, he said: "'I tied myself up.
"I did everything because when I realised I killed her, I thought of my child,"
The confession came as pictures of Anagnostopoulos hugging Ms Crouch's distraught mother at her memorial service on Wednesday were released.
The embrace took place as detectives arrived to call him away from the service - claiming they had arrested a new suspect and needed his help to identify him.
However, the suspect was Anagnostopoulos himself.
Police saw through his lies after data collected from a fitness tracker on Ms Crouch's wrist showed her heart had stopped beating before the alleged break-in took place.
Tracking data from Anagnostopoulos' home also showed him moving from the attic to the house's basement and back again, despite his claims to have spent all night tied to the bed.
Data from a security camera at home also showed its memory card had been purposely removed at 1.20 am - again, hours before the alleged break-in took place.
A senior detective working on the case said it did not take Anagnostopoulos long to confess.
"He said he had been fighting with Caroline for some time, and they were fighting that night, exchanging heated text messages while he was on the ground floor and she was in the attic," they said.
The investigator said that when Caroline texted her husband that he was "mad" he lost his "cool".
"He impaired the home's surveillance camera, removing its memory card, before storming up to the attic and smothering her to death," the police officer added.