Paul Henry, who was arrested two days after an incident in which Claire Boswell suffered life-threatening knife injuries her Glentham Road home, admitted to officers that he stabbed her.
But during a taped interview at Lincoln’s West Parade Police Station which was played to the jury, he said: “I think it was an accident - I didn’t do it on purpose.”
“I was just frustrated. I was just upset with everything. I didn’t want to kill her or anything like that. I can’t believe I’ve done it.”
Det Con David Haddock told the jury that the interview was ended after Henry became emotional and started asking questions about Miss Boswell’s condition.
Henry, 46, formerly of Lea Place, Gainsborough, denies attempted murder. He also denies an alternative charge of wounding with intent to cause Miss Boswell, 44, grievous bodily harm.
Robert Underwood, prosecuting, said Miss Boswell, a mother of three, had been harassed by Mr Henry for three or four years before he stabbed her on 15 September 2011.
The trial continues.