Johnny Cash to June Carter Cash
The fire and excitement may be gone now that we don't go out there and sing anymore, but the ring of fire still burns around you and I, keeping our love hotter than a pepper sprout.
Marilyn Monroe to Joe DiMaggio
I don't know how to tell you just how much I miss you. I love you till my heart could burst. All I love, all I want, all I need is you—forever. I want to be just where you are and be just what you want me to be. I know it's lousy of me to be so late so often, and I promise to try a million times harder, I promise. Love, Marilyn 
F. Scott Fitzgerald to Zelda Fitzgerald
Darling heart ambition enthusiasm and confidence I declare everything glorious this world is a game and while I feel sure of you love everything is possible I am in the land of ambition and success and my only hope and faith is that my darling heart will be with me soon.
Orson Welles to Rita Hayworth
Dearest Angel Girl:
...I suppose most of us are lonely in this big world, but we must fall tremendously in love to find it out. The cure is the discovery of our need for company—I mean company in the very special sense we've come to understand since we happened to know each other—you and I. The pleasures of human experience are emptied away without that companionship—now that I've known it; without it joy is just an unendurable as sorrow. You are my life—my very life. Never imagine your hope approximates what you are to me. Beautiful, precious little baby—hurry up the sun! Make the days shorter till we meet. I love you, that's all there is to it.
Napoleon Bonaparte to Josephine de Beauharnais
I don't love you, not at all: on the contrary, I detest you. You're a naughty, gawky, foolish Cinderella. You never write me; you don't love your own husband; you know what pleasures your letters give him, and yet you haven't written him six lines. Of what sort can be that marvelous being, that new lover that tyrannizes over your days and prevents your giving any attention to your husband? Some fine night, the doors will be broken open, and there I'll be. [November 1796]
Abigail Adams to John Adams
I dare not express to you at 300 hundred miles distance how ardently I long for your return. I have some very miserly Wishes; and cannot consent to your spending one hour in Town till at least I have had you 12. The Idea plays about my Heart, unnerves my hand whilst I write, awakens all the tender sentiments that years have encreased and matured, and which when with me were every day dispensing you. [October 16,1774]
Richard Nixon to Pat Nixon
...And when the wind blows and the rains fall and the sun shines through the clouds (as it is now) he still resolves, as he did then, that nothing so fine ever happened to him or anyone else as falling in love with Thee—my dearest heart.
Heloise to Abelard
I cannot live if you will not tell me that you still love me; but that language ought to be so natural to you, that I believe you cannot speak otherwise to me without violence to yourself. And since by this melancholy relation to your friend you have awakened all my sorrows, 'tis but reasonable you should allay them by some tokens of your unchanging love.