The married lover of Angelika Kluk denied he ever considered that his wife had played a part in the Polish student's death.
Mr Macaskill left the court in tears on Friday
Chauffeur Martin MacAskill, 40, told the High Court in Edinburgh that the idea "disgusted" him and had never crossed his mind.
The suggestion was made by Donald Findlay QC, who is defending the man accused of causing Miss Kluk's death.
Peter Tobin, 60, a church handyman, denies raping and murdering her.
The body of Miss Kluk was found under the floor of St Patrick's Church, in Anderston, Glasgow.
Mr Findlay put it to the witness that Miss Kluk was dead within hours of his wife deciding to "leave the marital bedroom".
'Patch things up'
Addressing the witness, he said: "Mr MacAskill, in your darker moments, when you have been sitting looking back on this, reflecting on all that has happened, did it never cross your mind that it was at least possible that your wife might have had some part to play in the death of Angelika?"
Mr MacAskill replied: "Never. The question, the suggestion, disgusts me."
The defence suggestion came after Mr MacAskill admitted that his wife, Annie, became angry and depressed when she found out about his affair with the Polish student almost half his age.
The witness admitted having "sexual intimacy" with Miss Kluk at his home within a week of getting to know her.
Jurors heard that Mrs MacAskill urged him to sever all contact with Miss Kluk and had hoped that she and her husband could patch things up.
But the court heard that Mr MacAskill decided he could not give up his relationship with Miss Kluk.
Angelika's body was found under the church floor
Mr Findlay put it to the witness that his wife became "upset" and "hurt" to discover that he was using with Miss Kluk the same term of endearment he used for her, and she decided to move out of the bedroom they shared.
The discovery was made after a trip the married couple made to Majorca in September last year to get some thinking space, the court heard.
Mr Findlay said that within a number of hours of that happening, "Angelika Kluk was dead".
Earlier Mr MacAskill had told the court of how he became frantic with worry when Angelika suddenly stopped responding to his texts and phone messages.
The next day he eventually got into her room and found all her belongings still there and decided to call the police.
The murder charge against Mr Tobin alleges that between 24 and 29 September of last year at the church in William Street, he raped Angelika, battered her with a piece of wood or something similar and repeatedly struck her with a knife.
It is alleged that he then hid the body under the floor of the church in an attempt to defeat the ends of justice.
He denies all charges against him. In a "special defence" Mr Tobin has admitted having sex with the Polish student, with her consent.
He has been accused of further offences of giving a false name and a breach of the peace.
The trial continues.