Milner was an old flame, he told the court today, saying they had been together for about five years before splitting up around 2002 or 2003.
When Mr Nisbet died, he was with another woman, and said he had not spoken to Milner for around 12 to 18 months until she phoned the next day to say he had died.
After going to the funeral, he was soon suggesting to her that they get back together. Three weeks after the death, which police originally ruled as a suicide, Mr Hayton told her that he loved her.
Mr Nisbet's elderly parents from Australia had been staying with her while they attended the funeral.
When they went back home on May 24, Milner texted Mr Hayton to say she had found a ``confession suicide note''.
She said Mr Nisbet had found out his youngest son Ben wasn't his, and that he had been cheating and the other woman had been blackmailing him. Mr Hayton told the court that he never saw the note.
The court has heard from numerous family members and friends of the deceased and the accused that they thought the suicide note shown to them by Milner was a forgery.
Milner denies murdering Mr Nisbet on May 4, 2009, as well as attempting to kill him twice on April 15, 2009.
The Crown says Milner was unhappy in her marriage and was motivated to murder by the prospect of cashing in the $250,000 life insurance policy.
She plotted the best ways to kill her husband - buying drugs under false names, asking friends for views on poisoning methods and even offering to pay $20,000 for a hitman to kill Mr Nisbet, it is alleged.
Mr Hayton split up with his then partner on May 28, spent a week at his bach at Motunau in North Canterbury, before moving in to the Checketts Ave, Halswell home that Milner owned in early June.
He was asked today by Crown prosecutor Brent Stanaway about an engagement ring the court has heard was bought by Milner at a Christchurch mall on July 12, 2009 - two months after her husband's death.
Mr Hayton confirmed he paid for the $2299 gold and diamond engagement ring with Milner, but denied it signified them getting married.
Instead, he claimed it was a ``friendship ring'', which drew laughter from a packed public gallery, made up of family members of Mr Nisbet and Milner.
Asked what finger the `friendship ring' was worn on by Milner, Mr Hayton said: ``Um, trying to think, probably wedding finger, something around there. I'm not sure - I didn't put it on the finger, I'm sorry.''
Earlier, the court heard that Mr Nisbet was an "anxious individual'' but was not suicidal.
Mr Nisbet's GP Dr Neil Beumelbury from Moorhouse Medical Centre gave evidence this morning in the trial.
Dr Beumelbury said Mr Nisbet had sought his help in 2007 for an anxiety-related disorder.
But he told the jury this morning that although Mr Nisbet was an ``anxious individual'' he did not speak of having suicidal thoughts and in his opinion was not suicidal.
In 2008, when Dr Beumelbury saw him for a driver's medical certificate he noted that Mr Nisbet appeared "very well and happy''.
He was given the antidepressant Citalopram to treat his anxiety in 2007 but the doctor said he believed he hadn't started the medication.
Toxicologist Dr Sarah Russell told the court that in the three fatalities linked to an overdose of Phenergan, blood levels ran from 2.4 milligrams per litre to 12 milligrams per litre.
Mr Nisbet had 0.7 milligrams per litre.
Forensic pathologist Martin Sage said there was no "tablet slurry'' found in Mr Nisbet's stomach contents but its absence in no way indicated it was not an overdose as it could have been absorbed.
He told the court there were far more efficient medications to take for an overdose which were readily available and would require lower amounts.
He said Mr Nisbet's death would have occurred quickly and said he estimated his death to have occurred at least eight hours before his post-mortem on May 4, 2009.
Speaking via video-link from Australia, Professor Ian White, a clinical toxicologist and pharmacologist, said the extremely bitter taste from the ground-up tablets would be hard to disguise.
"It would have been difficult to disguise unless it was a very hot curry like vindaloo,'' said Professor White.
The trial before Justice David Gendall continues, with the final Crown witness due to give evidence.
