The inside story of how Eric Clapton sneakily stole his pal George Harrison’s first wife, Pattie Boyd, has finally been revealed. In her upcoming autobiography, “Wonderful Tonight,” Boyd, a former London model, says her 10-year storybook marriage to the beloved Beatle collapsed after she received an unexpected love note from Clapton. “One day, I got a letter in the mail. It was written on a piece of paper torn out of a copy of the novel ‘Of Mice and Men,’ ” writes Boyd, the inspiration both for Harrison’s most famous song, “Something,” and for Clapton’s “Layla.” “In tiny, scrawly, little handwriting it said, ‘Dear Pattie, I have always loved you and this is breaking my heart. All I want is to be with you.’ So I showed it to George, who just dismissed it. Early that evening, the phone rang and it was Eric. He said, ‘Did you get my letter?’ ” Boyd launched into an affair with the guitar great and eventually dumped Harrison to marry “Slowhand” in 1977. That marriage would last 11 years, and through it all Clapton remained friends with Harrison, up to the Beatle’s untimely death in 2001.