Robert Rhodes, 43, said he acted in self-defence when he cut Dawn Rhodes's throat at the family home in Redhill, Surrey.
The carpenter told police she "came at him at speed" with a kitchen knife and as he disarmed her, he slashed her across the neck.
He was acquitted of murder following a retrial at the Old Bailey.
The court heard Mr Rhodes had learned his wife was having an affair with a married colleague the previous Christmas and the pair had decided to divorce.
During a row at their home in Wimborne Avenue in June, jurors were told Mrs Rhodes confronted her estranged husband about his new relationship.
Mr Rhodes claimed his 6ft, 14-stone wife grabbed the knife and came at him while making a "growling noise".
He said in disarming her, he swung the knife and slashed her across the neck, leaving a gaping 13cm wound.
Afterwards, he told police he had lashed out at his wife after she "flipped" like Marvel Comics character, the Hulk.
Jurors heard Mr Rhodes had allegedly threatened to kill the man his wife was involved with, who was named as Michael Cullen.
He was also said to have sent Facebook messages from a fake account to Mr Cullen's wife.
After the jury delivered its verdict, Judge Michael Topolski QC said: "Irrespective of the outcome, this has been a great tragedy for all. There are no winners, only losers."
He added: "I want my very last words in the case to be to the family of Mrs Rhodes. The court sends their condolences."
A man has been cleared of killing his unfaithful wife after she "flipped like the Hulk" during a furious row.