Interview: John Suchet, journalist

Bonnie Suchet has dementia. It may be Alzheimer's, it may not. She lives in a care home now. "She looked lovely yesterday," Suchet repeats wistfully, several times.

"She's still the beautiful woman I fell in love with, and knew all those years, but her character has changed. She is not the Bonnie that she was. She still has the same essential qualities of gentleness and calmness and quiet. She doesn't rant and rave. But I can't talk to her. We can't share things any more."

Instead, he is sharing her with the world by writing a book, My Bonnie, which is subtitled: "How dementia stole the love of my life."

It is hard to believe a person can simply disappear while they are still alive. That an impostor can come and squat inside the familiar shell of your loved one. Certainly, that is their body… their hair… their eyes… and yet, those eyes cannot reflect the nuances they once did.

There are only shadows of understanding now. You are uneasy around this imposter and how guilty that makes you feel. Because it is still them, is it not?

Shouldn't you connect in the same way? But conversation is stilted, in the way of two people who knew each other once, long ago, but do not speak the same language any more. Dementia steals a person long before death does. And you grieve for them before they've gone, hold a funeral in your heart for a person still alive.

"The most difficult thing I have had to deal with is that with this wretched disease, you are behaving as if the person you have lost is dead," says Suchet.

"Writing the book about her… it's as if she's dead." It's a brutal question: is death easier to handle than dementia? "With death, you close the door. With this, you can't close the door."

He had dinner with a friend a few months ago and after a few glasses of wine the friend said, are you going to get married again? "I said, what?!" A male friend then? Yes, says Suchet, and half laughs.

"But you can almost understand the question. The way I was behaving, with tears in my eyes, it's as if I was in mourning. I am behaving as if she's dead. But she isn't. She's my wife and I adore her and I saw her yesterday, so of course I'm not going to get married again. I couldn't."

Last September, 68-year-old Bonnie finally went into care and eventually he put their flat on the market.

He tells himself Bonnie has a new life now, so he must too. He has spent days sorting out her clothes, organising old paperwork.

"I was going through her life and shredding it… behaving as if she's gone. Then I went to see her and she said, 'Hell...oo!' I thought, do you know what I have just been doing? And of course, she didn't."

She is always pleased when he visits, has little tears in her eyes when she spots him.

She doesn't remember his second name, though. They have advice for visitors to the home: parachute in, evaporate out.

He and Bonnie were sitting on a sofa in the communal area when Bonnie suddenly got up and walked off.

"I grabbed my coat and left. No goodbyes. As I waited for the lift, I saw her walk past. She didn't look, didn't turn."

Outside the home, he called a taxi to take him to the station. It was the best visit with Bonnie he'd had yet, he told himself. Then he stood outside, waiting for the car, and cried like a baby.

There is the dementia story and the love story. One is sad, the other inspiring, but they overlap. It was the love story Suchet wanted to write.

He and Bonnie were neighbours when they met, each of them married. Suchet had three sons, Bonnie two. Suchet's first marriage was fractious, volatile.

His parents, to whom he was very close, had not wanted him to marry Moya and she never forgave them. When she and John married, she made him choose: her or them. Suchet didn't see his parents for several years.

Ironically, it was Bonnie, who said how sad and wrong that was, who inspired him to go round and heal the rift. When he and Bonnie finally got together, they loved living in the same block of flats as his parents. His mother delighted in having her boy back. She'd phone him up and invite him downstairs for a cup of tea.

Suchet, was brought up in London, studying at Dundee University before joining Reuters as a journalist, then the BBC and finally ITN, where he eventually landed the top job of US correspondent.

But his private life was in turmoil. Bonnie flew out for a secret meeting with him and they made a pact to be together. For Suchet, their affair was simply a coup de foudre. He was overwhelmed by this glamorous American blonde who reminded him of Grace Kelly. His marriage broke up shortly after, with his wife preventing him seeing his sons. Bonnie left her husband and she and Suchet married.

When Suchet was writing his book, Bonnie's illness had deteriorated to the stage where she simply walked up and down, and up and down, their flat all day long. Pacing the hall corridor, the living room.

As he wrote about the young woman he fell in love with, the picture in his mind could not have been more polarised from the evidence he now saw in front of his eyes. It shaped his writing.

The past and the present constantly intertwine throughout his narrative, flashing contrasting images of "then" and "now". Sometimes, the most thought-provoking writing is that which pushes you out of your comfort zone.

Suchet writes about a very sexy, passionate and intense relationship with Bonnie and then cuts away to scenes where he is now cleaning her, and the carpets, after yet another toileting accident. Lover to carer.

"Did you feel it was too much?" he asks anxiously. He is clearly on an emotional knife edge about this book. Sometimes he wishes he hadn't written it.

Sometimes he wishes he'd never taken that first decision, in February 2009, to go public on BBC breakfast news and reveal Bonnie's condition. But Suchet had the invaluable help of an Admiral nurse, simply because of where he lived, and he knew that wasn't right.

He is now honorary president of the charity Dementia UK, which campaigns for Admiral nurses. There are only 60 in the entire country, yet there are 700,000 dementia sufferers. One in three people over 65 will die with dementia and by 2050, estimates suggest there will be 1.7 million sufferers. Suchet knows how much needs to be done.

It all happened so quickly to Bonnie. She was super-organised before retiring from her job at the heart of a charitable worldwide foundation. But in 2004, she went off to the toilet at Stansted airport when they were waiting for a flight and couldn't find her way back. Suchet had to pick her up at the information desk. After that, life began to turn upside-down.

"Half of me wants to raise awareness," he groans. "That bloody expression. I want to speak out on behalf of carers, I want to campaign for Admiral nurses, blah, blah, blah, yet the other half of me wishes I had kept my mouth shut." He says the words slowly, with deliberation. "That I had just lived out anonymously with Bon, protected her from everything; kept quiet, and just quietly grieved while I slowly lost her."

The reaction to that first interview was massive – a tsunami, he says – with e-mails flooding in from China, Australia, South Africa, Canada, America. People logging on to the BBC from all over the world who were touched by his story. He knows now he speaks for many carers.

Yet there is one question he dreads being asked above all others. "What right do you think you have to tell the world about your wife, all those private, intimate details?" And how would he answer that question? "I don't know." He pauses. "I still don't know if I have done the right thing. I think if someone writes that I have done the wrong thing, then I just couldn't cope with it. I couldn't cope."

Someone will always say that. Always. It doesn't mean they're right. What would Bonnie have said? "If she was able to understand her illness, and able to understand that through me she was helping people, that would make her so happy. I know it would. Because I know the kind of woman she is. I know I'm a romantic but she always wanted to help other people."

Perhaps that's his answer then. "Do you think I should show her?" he says. "I would – except for that." He points to the subtitle, that word 'dementia'. Can she read still? "Not really. And if she read it, she probably wouldn't understand. But I could show her the pictures and say, 'Look darling, I wrote a book about you.'"

Yet there are things in that book that he is ashamed of. No carer will be surprised by them. The days where he was so stressed, he lost his temper.

Days when he was trying to clean up "accidents" and Bonnie didn't understand, when her constant walking, always two steps in front of him, drove him crazy. Sometimes, she resisted being undressed and washed and he once grabbed hold of her arm so forcefully to get her in the shower that he bruised it. And once she was so frightened by his sudden temper that she instinctively lashed out with her nails. Did he find all this hard to confess?

"Oh yes," he says, his voice low. Perhaps there is a certain bravery in describing yourself as you are. "Is there?" he says, almost bitterly. "I see it exactly the opposite. I think it's cowardly. It's a way of trying to get sympathy and owning up to atrocious behaviour."

He has learned as much about himself as Bonnie. Things he'd rather not know. "You find yourself behaving in a way you wouldn't necessarily think you would. You discover things you may not be terribly proud of. Does this mean that's what I am really like deep down and I didn't realise it? That there's a nasty streak? Or was it entirely brought on by the disease and the circumstances that disease caused?"