Stuart Gallear, 51, had admitted the manslaughter of Mandy Gallear, 42, in the kitchen of their home in Hindley, Wigan, but claimed he did not intend to kill her and lost his self-control.
A jury at Manchester Crown Court rejected his account and unanimously found him guilty of the murder on October 6 last year.
Police arrived at the couple’s home in Makinson Avenue within 10 minutes of the defendant ringing for an ambulance and found Mrs Gallear lying motionless on the kitchen floor with three deep wounds to her chest.
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Mrs Gallear, head of accounts at a property firm, was rushed to hospital but medics could not resuscitate her and she was pronounced dead.
Six months earlier Mrs Gallear confessed to her husband, a warehouse manager, about having an affair, but denied it was with joiner Mark Prescott and said it had ended.
However, on October 5 the son of Mr Prescott’s partner called at the Gallears’ front door and revealed the relationship was ongoing.
Following his arrest, Gallear said the couple talked “amicably” in the kitchen as he came home on the afternoon of October 6 after he drank five pints of lager in a local pub.
Gallear said his wife then said: “Anyway, it’s sorted now. We are separating. I love him more than you” and his memory of what happened next was “blurred”.
It was then he stabbed her three times.
He claimed his wife then protested “what are you doing? I still love you” and he then “just snapped out of it”, put the knife aside and rang for assistance.
The prosecution accused him of having “selective memory loss” and said the stabbing was the culmination of his anger and resentment which built up since he found out about the affair.
Gallear showed no emotion as the verdict was delivered.
Sentencing will take place on Wednesday April 12.