John Martin, 48, denies murdering Russian pianist Natalia Strelchenko, 38, at their Manchester home on their second wedding anniversary last August.
Manchester Crown Court heard he took the diazepam believing it to be his prescribed anti-depressant medication.
He said "everything is very blurry".
It is alleged the double bass player strangled and beat Ms Strelchenko, who was also known by the surname Strelle, in a loss of temper at their home in Newton Heath on 30 August.
Giving evidence, Mr Martin, also known as Jon Skogsbakken, said he had been suffering with depression and that he had unwittingly taken unmarked diazepam tablets for around six weeks.
He said he "guessed" they had been prescribed to his wife.
Mr Martin told the jury he had suffered with depression since 2005 and his GP would prescribe him Escitalopram.
He told the court that taking the diazepam was "the biggest mistake of my life".
Mr Martin said: "I would never have taken the two together, absolutely not", if he was aware the tablets could have a "paradoxical and aggressive response" and when taken with alcohol it could increase the effects.
The court heard following an argument with Ms Strelchenko, he drank four cans of cider at their home before going to the working men's club where he had another pint of cider and then returned home.
He said: "I just sat down on the floor and poured myself a glass of wine. I started to drink it. Natalia was angry because I was drinking wine and she tried to take it away from me.
"Everything is very blurry for me. I can't recall anything after that point.
"I still love her very much. I would never wish to do such terrible things to her. I recall virtually nothing."
Mr Denney QC said: "Do you accept that on evidence you killed Natalia?"
Mr Martin replied: "Well according to what the witnesses described...I perfectly understand that I must be the man behind it."
Mr Martin, who had worked for the computer firm IBM in his home country of Norway, met Ms Strelchenko in 2007.
She had performed piano recitals at New York's Carnegie Hall and London's Wigmore Hall.
The trial continues.
A musician accused of murdering his wife has told a court "I perfectly understand that I must be behind it" but recalls "virtually nothing" after taking diazepam and alcohol.