A teacher, who believed her "unfaithful" partner was cheating on her again, fatally stabbed him in the neck in their bedroom before burying his body in the garden, a court has been told.
Fiona Beal denies murdering Nicholas Billingham, whose partly mummified remains were found last March, four-and-a-half months after he was last seen at a business meeting.
The primary school teacher, 49, wrote about her ruthless "dark side" in a "chilling" confession as she explained how she hid a knife in a bedside drawer and got him to wear an eye mask before his pre-planned killing on the evening of 1 November 2021, prosecutors claim.
In a notebook, Beal penned that she thought 42-year-old Mr Billingham was cheating on her, and "had decided to kill him" by October 2021, Northampton Crown Court was told.
Prosecutor Steven Perian said Mr Billingham had cheated on her with other women whilst he was still in a relationship with the defendant. "She [Beal] believed he was cheating on her again," Mr Perian said.
Beal then came up with a plan to kill him, rather than leave him, and also how to explain his disappearance and her own absence from work following his killing, Mr Perian claimed.
The court heard Beal told her headteacher she had COVID and needed to self-isolate, and she was off work between 1 November 2021 - the day of the murder - and 12 November.
Beal told other people that Mr Billingham had left her for another woman, and she used his phone to send messages to friends and work colleagues pretending he was still alive, it is alleged.
In her "confession", prosecutors said, she wrote: "I have to confess. Ok here goes. October 2021. He spat on me and threatened me during sex. I thought about leaving but the things he said and did fuelled my dark side - I call her Tulip22, she's reckless, fearless and efficient. Ruthless."
'Moving a body is much more difficult than it looks on TV'
An entry in the notebook referred to 17 years of "him" being argumentative, mean, cruel and belittling, the trial heard. It continued: "I knew I couldn't let him get away with it. Halloween sealed it. He was vile.
"That night I planned. COVID rules meant I had a guaranteed 10-day isolation period from positive symptoms.
"I called [Beal's headteacher] on the Monday and said we'd tested positive and had symptoms. He went to work. Tulip22 smoked and planned. I'd planned it mentally so many times before.
"I had a bath. I left the water in. I encouraged the bath with the incentive of sex afterwards.
"While he was in the bath I kept the knife in my dressing gown pocket and then hid it in the drawer next to the bed. I brought a chisel, bin bag and cable ties up too.
"I got him to wear an eye mask. It was harder than I thought it would be. Hiding a body was bad. Moving a body is much more difficult than it looks on TV."
Apparent suicide note discovered
On 6 March 2022, Beal, who worked at Northampton's Eastfield Academy as a Year 6 teacher, checked into a Cumbria lodge near Kendal after informing her headteacher she was ill.
Police visited on 15 March and found her with superficial wounds along with an apparent suicide note and the notebook after being contacted by a worried family member, the court heard.
Northamptonshire Police were then informed and visited Beal's Northampton home, finding a bloodstained mattress in the basement, and an apparent blood stain on the bed frame in the master bedroom, the trial heard.
Part of the back garden was also dug up, revealing "partially wrapped and partially-clothed" human remains.
Clothing thought to be a dressing gown was recovered, along with black plastic wrapped around the victim's head.
A pathologist concluded that the cause of Mr Billingham's death was a single stab wound to the right-hand side of his neck.
The trial continues.