Beethoven dedicated one of his most famous works - known today as the "Moonlight Sonata" - to Countess Giulietta (Julia) Guicciardi. His letters leave no doubt he was in love with her.
On the 6th of July (presumably, in 1801), Ludwig wrote the following anguished words to her:
My Angel, My All, My Very Self,
Just a few words to-day, and only in pencil . . . Can our love endure otherwise than through sacrifices, through restraint in longing. Canst thou help not being wholly mine, can I, not being wholly thine. Oh! gaze at nature in all its beauty, and calmly accept the inevitable - love demands everything, and rightly so. Thus is it for me with thee, for thee with me, only thou so easily forgettest, that I must live for myself and for thee - were we wholly united thou wouldst feel this painful fact as little as I should . . .
Now for a quick change from without to within: we shall probably soon see each other, besides, to-day I cannot tell thee what has been passing through my mind during the past few days concerning my life - were our hearts closely united, I should not do things of this kind. My heart is full of the many things I have to say to thee - ah! - there are moments in which I feel that speech is powerless - cheer up - remain my true, my only treasure, my all !!! as I to thee. The gods must send the rest, what for us must be and ought to be.
Beethoven scholars (including the respected biographer Alexander Wheelock Thayer) believe that Ludwig proposed to Giulietta and that she was inclined to accept. One of her parents, however - likely her father - would not allow it:
A careful survey and comparison both of the published data and of the private traditions and hints gleaned during a residence of several years in Vienna, result in the opinion (an opinion, note, not a statement resting on competent evidence) that Beethoven at length decided to offer Countess Julia his hand; that she was not indisposed to accept it; and that one of her parents consented to the match, but the other, probably the father, refused to entrust the happiness of his daughter to a man without rank, fortune or permanent engagement; a man, too, of character and temperament so peculiar, and afflicted with the incipient stages of an infirmity which, if not arrested and cured, must deprive him of all hope of obtaining any high and remunerative official appointment and at length compel him to abandon his career as the great pianoforte virtuoso. As the Guicciardis themselves were not wealthy, prudence forbade such a marriage. (Thayer's Life of Beethoven, Volume 1, page 292.)
When she did not have approval to marry Beethoven, Julia married Count Wenzel Robert Gallenberg (also a composer) instead.
Beethoven's Letter to "Immortal Beloved"
Translation of "Immortal Beloved" Letters
The "Moonlight Sonata," played at a fast tempo (2/2 adagio sostenuto)
The "Moonlight Sonata," played at a slow tempo
Antonie Brentano (alleged, by some historians, to be the "Immortal Beloved")
Portrait of Beethoven, commissioned by Franz and Antonie Brentano
Portrait of Karl, Beethoven's nephew