Anna Guy told The New Zealand Herald the trust she and her husband developed since they met when she was 15 had been betrayed by Macdonald's lies.
"Now you think ... Now I feel like a fool; it was total betrayal."
Ms Guy, who returned to her maiden name after her husband's trial for the murder of her brother Scott, told how she still struggled to comprehend the actions of Macdonald.
"I have known about stuff for a while but it is still a shock even now.
"I think that's why it was really devastating at the time because I found out so much more about him that I didn't know.
"It took me most of last year to get my head around it," she said.
"Getting arrested for killing Scott was one thing but there was way more stuff to come that was so devastating that no-one knew about."
Macdonald was jailed on Friday for five years on charges of theft, intentional damage, arson and graffiti.
He will be eligible for parole in December having already served 17 months.
Ms Guy said the situation seemed "unreal" and there were times when she thought she would go insane if she thought too much about it.
"But I have managed to switch off a bit now because I figured I would go insane if I thought about it all the time.
"But I keep going over and over conversations I had with him earlier. What did he actually mean by that?
"I mean, we did things together ... What did that mean to him? Was it real? You start to doubt.
"He had been through so much with us as a family. Then it was like he was a traitor, sort of."
And she admitted she still wonders if there are signs she should have spotted.
"That's the bit that is humiliating because I fully trusted him.
"You trust someone, especially when you have known them for that long. It was a double life and you think, well, the whole marriage was a sham."
The pair met at school and, after Macdonald started working on the Guy family farm, they married in 2001. Scott Guy was best man.
They have four children under 9 - Finn, Jack, Lucy and Wade.
Ms Guy said she was coming to terms with life as a solo mother.
"Finn and Jack feel it more than, say, 18 months ago.
"They have been a bit better now but they are a bit up and down." "It's hard when I do things like go to school and it's family day. The kids really notice it then."
Macdonald is allowed to phone his children from prison, but Ms Guy said there were no set times.
She will let them visit only once a month because "I don't want them to get used to going there. It is not a place for children, but he is their father."
She revealed she had asked Macdonald several times whether he killed her brother and he always said no.
Ms Guy said her relationship with Macdonald was over by the end of his murder trial and she was no longer in love with him.
"It was pretty much me choosing my family or him at the end of the day.
"And he knew how important my family was to me too.
"I think, now I have thought about it, I have a soft spot for him. I did love him but I am definitely not in love with him.
"I think things have changed so much. I think the 'friend' is what I knew, not the other Ewen who I didn't know.
"I mean we kind of just grew up together and that's where we have the history."
Ms Guy said she was not in a new relationship despite rumours to the contrary.
She had been in a "brief" relationship last year but that had ended and she was single.
Ms Guy said was considering leaving Feilding for Auckland.
"I want more. I understand it will be hard for the kids if we left, but I have done a lot of hard stuff over the past few months so I feel I can cope with anything.
"You know through this tough time I feel I have got through the worst of it, so if I can handle all of that crap I can definitely take on anything that I put my heart to.
"If you are really passionate about something, you can do anything."
Scott Guy's widow, Kylee, has reportedly signed a magazine deal worth up to $60,000 and may be negotiating a book contract.
Sensible Sentencing Trust's Garth McVicar confirmed Mrs Guy had been negotiating magazine and book deals for a while.
"I'm aware there are negotiations going on ... There is a book deal around but that is confidential stuff," he said.
By Carolyne Meng-Yee
