Pattie's relationship with George began to decline after The Beatles' trip to India in early 1968.
George had become obsessive about meditation. He was also sometimes withdrawn and depressed.
My moods started to mirror his and at times I felt almost suicidal. I don't think I was ever in any real danger of killing myself but I got as far as working out how I would do it: put on a diaphanous Ossie Clark dress and throw myself off Beachy Head.
In March 1970, George and Pattie Harrison moved into a new house - Friar Park, a Victorian Gothic mansion near Henley-on-Thames, Oxfordshire.
That whole period was insane. Friar Park was a madhouse. Our lives were fuelled by alcohol and cocaine, and so it was with everyone who came into our sphere. We were all as drunk, stoned and single-minded as each other. Nobody seemed to have appointments, deadlines or anything pressing in their lives, no structure and no responsibilities.
George's attentions often wandered to other women, and Pattie knew that he was unfaithful to her - most notably with Ringo Starr's wife Maureen.
She was the last person I would have expected to stab me in the back. I discovered from some photos that she had been staying in the house with George while I had visited my mother in Devon. He had given her a beautiful necklace, which she wore in front of me.
Then I found them locked in a bedroom at Friar Park. I stood outside banging on the door yelling: 'What are you doing? Maureen's in there, isn't she? I know she is!' George just laughed.
Eventually he opened the door and said: 'Oh, she's just a bit tired so she's lying down.'
I went straight to the top of the house and lowered the flag bearing the om symbol that George had been flying from the roof and hoisted a skull and crossbones instead. That made me feel much better.
Maureen wasn't even prepared to be subtle. She would turn up at Friar Park at midnight and I would say: 'What the hell are you doing here?' 'I've come to listen to George playing in the studio.' 'Well, I'm going to bed.' 'Ah, well, I'm going to the studio.'
Pattie's relationship with George Harrison steadily declined during the early 1970s. He was often unfaithful towards her; she, meanwhile, was being pursued by Eric Clapton.
I was aware that Eric found me attractive and I enjoyed the attention he paid me.
It was hard not to be flattered when I caught him staring at me or when he chose to sit beside me. He complimented me on what I was wearing and the food I had cooked, and he said things he knew would make me laugh. Those were all things that George no longer did.
Although she had previously succumbed to Clapton's advances, Pattie remained with George Harrison for several years as their relationship faltered. One night, at a party at the home of pop impresario Robert Stigwood, Clapton had confessed to Harrison his feelings towards Pattie.
During the early hours, George appeared. He was morose and his mood was not improved by walking into a party that had been going on for several hours and where most of the guests were high on drugs.
He kept asking 'Where's Pattie?' but no one seemed to know. He was about to leave when he spotted me in the garden with Eric. It was just getting light, and very misty. George came over and demanded: 'What's going on?' To my horror, Eric said: 'I have to tell you, man, that I'm in love with your wife.'
George Harrison's marriage to Pattie ended in June 1974, and she took up with Eric Clapton. Despite this, the two guitarists remained close friends.
The first Christmas after I'd left him, in 1974, just as Eric and I were sitting down to lunch, George burst in, uninvited. He had some wine and Christmas pudding with us. I couldn't believe how friendly he and Eric were towards each other.
The sad thing was, I realised later, he wasn't doing anything on Christmas Day and must have been lonely.
Clapton wrote Layla for Pattie; the song detailed his unrequited love for her, and was inspired by a Persian tale that Clapton had been given by a friend. He also wrote Wonderful Tonight for her on 7 September 1976, while waiting for her to get ready to attend Paul and Linda McCartney's annual Buddy Holly party.
The couple remained together for several years, in spite of Clapton's heroin and alcohol addictions and numerous infidelities, but eventually divorced in 1989 following his affair with Italian model Lori Del Santo.
George Harrison died of cancer on 29 November 2001. The loss profoundly shocked Boyd, who had remained close to him in the years after their marriage ended.
I burst into tears when I heard he had died; I felt completely bereft. I couldn't bear the thought of a world without George.
When I left him for Eric, he had said that if things didn't work out, I could always come to him. It was such a selfless, loving thing to say.
Now that sense of security had gone. At the end I hadn't grasped how ill he was as I hadn't seen him for a few months. The last time had been at my cottage: he had phoned to say he was coming to Sussex to visit Ringo and Barbara and wanted to see me - I think he was curious to know where I was living. I was so glad we'd had that last meeting.
On 14 February 2005 an exhibition of photographs taken by Boyd during her time with Harrison and Clapton opened at the San Francisco Art Exchange. It was titled Through The Eye Of A Muse. It was repeated in San Francisco in February 2006, before moving to London.
Her autobiography Wonderful Tonight, written with journalist Penny Junor, was published in August 2007.