Tony Vita, 47, told the High Court in Glasgow that Marion Vita begged him not to take his own life and tried to hide the blade from him.
He said that after he fell on the floor his wife stepped back with the knife behind her back and fell on the couch.
Mr Vita said she then sat with her head bowed and told him to "go up and finish it" and he took the knife from behind her back and went up to his room and tried to commit suicide.
Mr Vita denies murdering his wife last September 20 at their home in Baillieston, Glasgow, after learning she was having a lesbian affair.
In evidence Vita said he was devastated when he found out about his wife's infidelity and sent her a string of text messages the night before the alleged killing and on the day. He told the court he planned on killing himself and that he told Mrs Vita this.
The jury heard that on the day of the alleged murder Mr Vita took a cocktail of pills and drank a bottle of vodka with the intention of then using a knife to end his life.
He said that after taking them he was woken by Mrs Vita who was shaking him and slapping him on the face and asked him if he had drank anything. He said she saw the knife on the bedside cabinet and asked him what it was for and he told her his intention was to kill himself.
The court heard he questioned his wife about her relationship. Mr Vita said: "It was just a normal discussion, it wasn't heated or anything like that. Marion looked upset."
He said that after they finished talking he went into the kitchen and picked up the knife but tried to hide it from his wife when he walked back into the living room.
The court heard Mrs Vita grabbed her husband's dressing gown sleeve and as he forcefully pulled his arm away he lost his balance and fell on the floor and dropped the knife. He said his wife picked it and held it to her chest.
He said he grabbed her arms and told her to calm down but that he then fell on the floor again.
Mr Vita said he got up from the floor and at that Mrs Vita stepped back with the knife behind her and fell back on to the sofa, then sat up. He said: "She just sat there with her head bowed."
He said he took the knife upstairs and tried to push it into his body but couldn't get the knife in, and the next thing he can remember was being taken away to hospital.
Under cross-examination Mr Vita was asked: "Who did stab Marion in the back?" He replied: "I am assuming it was as a result of the struggle."
The trial continues.