Forty-two-year-old Susan Colquhoun knifed 30-year-old Alan Kopp in the flat they shared in Hillhouse, Hamilton, on January 9.
But afterwards she denied having anything to do with his death and claimed Mr Kopp had come home fatally injured after being attacked in the street.
Colquhoun was only brought to justice after the friend she confessed her guilt to finally came forward – three months after the killing.
The High Court in Glasgow heard that a massive police investigation was launched and 400 witnesses statements were taken.
The police quizzed Colquhoun on three separate occasions, but she never deviated from her story.
The breakthrough came when a friend of Colquhoun's was interviewed again in April and admitted Colquhoun had confessed to the killing
Yesterday, Colquhoun, who was originally charged with murder, pled guilty to a reduced charge of culpable homicide.
She also admitted attempting to defeat the ends of justice by washing her bloodstained hand, wiping blood from the knife used in the killing and throwing it from the balcony of the flat.
Judge Lady Stacey deferred sentence until January 10 at the High court in Edinburgh.