"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'd go insane if she thought too much about it.
"It's really terrible. I am not very good if I sit down or lie down in bed for too long with nothing to do because I start thinking. It's like a nightmare.
"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.
"I never looked at his phone. I never checked what he was doing ... 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. They will have really good patches then they might have one thing happen that would make them feel very upset.
"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 so it's the "luck of the draw" if he gets to talk to them.
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."
The children sometimes ask when dad is coming up but Ms Guy puts them off because she feels bad that she doesn't have an answer for them.
Ms Guy was a witness during the murder trial and broke down in tears after Macdonald was acquitted.
She said she was concerned what people might have thought of that, but said she would have cried whatever the verdict as she was simply "overwhelmed".
And she revealed she has asked Macdonald whether he killed her brother. She said she had asked him several times and he always said no.
Speaking before last Friday's sentencing, Ms Guy said she had waited until the end of the murder trial to revert to her maiden name to avoid "tongue-wagging".
There was never any doubt that the relationship was over by that time.
"It was funny how many people would think, 'Oh gosh, maybe she should, you know, stay with him'.
"I am surprised people would think that. I think people have forgotten what he has done.
"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."
Ms Guy said she was no longer in love with Macdonald.
"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.
Macdonald will face his first parole board hearing in December - something that has angered the Sensible Sentencing Trust, which says the sentence sends all the wrong messages.
The Parole Board says 90 per cent of offenders are declined parole at their first hearing date, which is generally an opportunity to assess an offender in terms of what rehabilitation they need in prison.
Regardless of when he is released, Ms Guy said Macdonald's future was uncertain. He is unlikely to travel overseas because of his conviction and his family here, but he will also struggle to start afresh after such high-profile offending.
On the other hand, Ms Guy is now preparing to look for a more positive future. She is only 31 and said she had a whole life ahead of her.
And she is considering leaving Feilding for Auckland.
"You know, one day the kids will grow up, leave home, study and get jobs. I will be left on my own here.
"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.
"I love this house but you realise possessions don't make you happy. It's the simple things. I feel it's time to start thinking of me now.
"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."
The Guy murder case
2010
* Jul 8: Scott Guy fatally shot twice in his Feilding driveway.
* Jul 16: Mr Guy's funeral held, with Ewen Macdonald among pallbearers.
* Jul 20: Vandalism attacks on Mr Guy's property revealed.
* Jul 21: Police say three labrador puppies went missing from Mr Guy's property around time he was killed.
2011
* Apr 7: Macdonald charged with Guy's murder and pleads not guilty.
2012
* Jul 3: Macdonald acquitted of murder. New charges revealed, including arson, criminal damage.
* Sep 10: Scott's widow Kylee begs the Attorney General to ensure Macdonald receives a lengthy sentence for the new charges.
* Sep 14: Macdonald jailed for five years.
