David Browning, 52, was jailed after being found guilty of killing his payroll department boss, Jillian Howell.
The 46-year-old Samaritans volunteer was found covered in blood on the floor of her lounge, with 15 stab and slash wounds.
Sentencing him, Judge Christine Laing QC said the way in which he murdered her was “savage”, adding: “This was a sustained attack and the terror and trauma for her in the final few minutes of her life is unimaginable.”
During the trial, the court heard how she was knifed in the chest, abdomen and neck before Browning wrote “bully” on her with a marker pen.
The jury heard how Browning, Ms Howell’s deputy at the University of Brighton payroll department, formed an “intense attachment”, sending her gifts and flowers and becoming “possessive, controlling and jealous”.
Despite not feeling the same way, Ms Howell continued to try to help her colleague with his mental health problems.
The killer – a married father of two – told Ms Howell about his suicidal thoughts as he was preparing to leave her home on 25 October after she had cooked him dinner.
She told him he needed to get help at hospital, and when she bent down to put on her shoes Browning said a “whoosh” came over him and he stabbed her in the back.
He told the court she grabbed the knife, screaming “You b******” – to which he replied: “I’m sorry Jill, this is what mental health does to you.”
Browning, who had also brought a change of clothes and a shotgun with him, put the weapon to his throat but was unable to fire the weapon.
He stayed in the house for “several hours” after the 25 October murder – even finding time to post a cartoon on Facebook with the slogan “Stand up to bullies, then kill them”.
Police found out about the murder when Browning called emergency services from outside a police station to say he had a gun, was suicidal and should be sectioned under the Mental Health Act.
Inside the station, he told them: “In a nutshell, I’ve killed my boss.”
Officers found her body in the home along with a note from Browning which was intended to be a suicide note.
Browning was convicted by a jury at Hove Crown Court after deliberation of just two hours and 20 minutes.
Ms Howell’s family described her as a “gentle and kind soul”.