Wonderful Tonight

Pattie Boyd was married to George Harrison of the Beatles. Eric Clapton of the Yardbirds, the Bluesbreakers, Cream, Blind Faith, and Derek and the Dominoes was in a relationship with Charlotte Martin, a French model. The two couples were quite close, and before long Charlotte got close to George (though nothing came of it) and Eric wrote a love letter to Pattie (in all lowercase):

dearest l,
as you have probably gathered, my own home affairs are a galloping farce, which is rapidly degenerating day by intolerable day . . . it seems like an eternity since i last saw or spoke to you! . . . (He wanted to know her feelings, and asked specifically if she had feelings for him, and to write back quickly.) please do this, whatever it may say, my mind will be at rest . . . all my love, e.
(Taken from "Wonderful Tonight: George Harrison, Eric Clapton, and Me")

Needless to say, their relationship was changed forever. Some time after, they met secretly where he played the song "Layla." She knew immediately that the song of unavailable love was about her. She went to a party with Eric, and when George walked in, Eric said "I have to tell you, man, that I'm in love with your wife." By that time, George and Pattie's marriage was falling apart, so Pattie left him for Eric in 1975.  They married in 1979. After that point, their marriage was filled with drugs, alcohol, and infidelity. Despite that, she inspired songs such as (officially) "Layla," "Bell Bottom Blues," and "Wonderful Tonight," (and unofficially) "She's Waiting," "Why Does Love Got To Be So Sad," "I Looked Away," "Keep On Growing," and "Have You Ever Loved A Woman."They divorced in 1988.