James McCarten, 51, battered 43-year-old Anna Rosenberg after finding her and 62-year-old Alan McLean together at his flat in Glasgow on 2 May 2015.
The victim suffered 122 injuries and was described in court as being “pummelled to a pulp”.
McCarten, who was convicted of Ms Rosenberg’s murder, was told he must serve a minimum of 15 years in jail.
During a previous hearing at the High Court in Glasgow, McCarten was also convicted of trying to cover up the murder and assaulting Mr McLean.
‘Slow death’
Jailing him at the High Court in Edinburgh, judge Kenneth Maciver QC told McCarten: “It is clear from the injuries which Miss Rosenberg sustained, and from the evidence of the pathologist, that these injuries led to restriction of her ability to breathe.
“When it must have been obvious that she was dying a slow and painful death, you did nothing to assist and within a couple of hours thereafter you changed clothes and left the house to watch, of all things, a boxing match.
“You attempted to clean up the blood and the bedding, and you dressed and moved her body and you gave the emergency services and the police a false account of what had happened to her.”
The judge added: “This demonstrates a callous and heartless disregard for her and a selfish desire to avoid responsibility for the savage onslaught of violence which brought her life to an end.”
The court previously heard that McCarten had been in a relationship with Ms Rosenberg for about 18 months.
The victim, who was from Bearsden, East Dunbartonshire, often stayed over at his flat in Maryhill.
The jury heard that McCarten had allowed fellow builder Alan McLean to stay with him after he had split up from his partner.
While McCarten was out of his flat, however, Mr McLean and Ms Rosenberg had sex.
The 62-year-old told the court how he tried to put on his clothes when McCarten returned home as a terrified Ms Rosenberg lay in bed.
Mr McLean recalled: “He was shouting and bawling ‘how could you do this to me’.
“Anna kept saying she was sorry, she was crying. James was upset, but that was understandable.”
Mr McLean said McCarten went on to headbutt him – after asking him to take his glasses off.
McCarten then kicked his friend out of the flat before launching a brutal attack on Ms Rosenberg.
The trial heard how the victim, whom he also tried to throttle, suffered 122 injuries, including multiple fractured ribs.
‘Saw red’
McCarten later left the flat to watch a boxing match at a friend’s house.
The killer claimed he only realised Ms Rosenberg was dead when he returned the next day.
He offered to plead guilty to the reduced charge of culpable homicide, saying that he loved Ms Rosenberg and did not “realise the extent” of his attack.
McCarten admitted he “saw red” and “unleashed” a “lot of blows” on the victim but did not intend to kill her.
But the jury convicted him of murder after hearing how Ms Rosenberg had been “pummelled to a pulp” and how McCarten tried to clean up the flat and put clothes on her afterwards.
