Tragic cameraman Billy took his own life last year aged 40 after being ravaged by depression.
He was said to have given Zoe, 47, a “new lease of life” after her split from DJ and record producer Fatboy Slim, aka Norman Cook, the father of her two children, but was unable to battle the demons in his head.
Speaking publicly for the first time about her loss she said: “At the time Billy came into my life, I didn’t know how to help.
“I knew he had lived with depression for a long time. But he was a big strong guy.
“He did the Iron Man, he loved cycling 50 miles a day, he was the life and soul of the party when he was on the crew, he was so much fun.
“To see a man like that crumble under the pressure was heart-breaking to watch.
“I knew how much pain he was in. He couldn’t make sense of what was happening to him.
“It was almost like a change of light, you could see the pain come into his eyes.
“You wanted to say, ‘Come on. Stay with me, stay with me. Let’s get you out of this headspace’.
“But it was harder and harder to do that.”
Last week Zoe, who fronts the spin-off show Strictly Come Dancing: It Takes Two, finished a gruelling 350-mile cycling marathon for Sport Relief to raise money for those battling mental illness.
Her journey took her from her birthplace in Blackpool to her hometown of Brighton via Billy’s native Darwen in Lancs., and was called the Hardest Road Home.
It is hoped her efforts will have raised £500,000.
She tells Radio Times, on sale today: “Billy didn’t tell me about his depression at the beginning, it’s only when you get to know someone that they really share stuff like that.
“Any other illness and you have time off work, but there is a lot of stigma around mental illness. It’s frightening to talk about it.
“The people suffering don’t want sympathy. Although I wasn’t surprised when he eventually told me.
“I could see there was some sadness. I tried my best to help. But I look back and think, ‘I’m not sure I did the right thing’.
“You can’t just sit down with someone when they are that poorly and say, ‘I want to help’. There is no quick fix.
“I’d say things like, ‘If you exercise, go outside, see someone you love, it might help’. But it didn’t. And the therapy he had didn’t even touch the sides.”
Around 6,000 families lose someone to suicide in the UK every year – the biggest killer of men in the UK under the age of 45.
Zoe said: “One in four of us will experience mental illness. But the number of young men killing themselves is shocking.
“Why? A lot of men I have spoken to have said it’s very confusing being a modern man.
“You want to be sensitive but also strong. You can’t win. It’s really hard trying to be both.
“Yes, this a disease, and men suffering with depression need help.
“It takes the right person to break through to someone who has been brave enough to reach out.”
Zoe, the daughter of Maths genius Johnny Ball, started dating Billy, who worked on Antiques Roadshow, after separating from 54-year-old Mr Cook, her husband of 17 years, and father of her son Woody, 17, and daughter Nelly, eight.
Billy was found hanged in his flat in Putney, south west London, in May and was pronounced dead after paramedics were unable to revive him.
Zoe said: “Even now I sometimes think, ‘I’m a resourceful woman, I’m a bright woman…why could I not save him?’ And then I have to stop and say, everyone who loved him knew.
“None of us found an answer, none of us saved him. To move forward you have to accept that. Which is very difficult.
“But I take comfort from the fact he is no longer in pain. He struggled every day and now he is at peace.
“The pain has stopped for him.”
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