It's about John Keats and his love, Fanny. I adore this movie.
Here is a section of a letter from John to Fanny, found here.
Upon my Soul I can think of nothing else - The time is passed when I had power to advise and warn you again[s]t the unpromising morning of my Life - My love has made me selfish. I cannot exist without you - I am forgetful of every thing but seeing you again - my Life seems to stop there - I see no further. You have absorb'd me. I have a sensation at the present moment as though I was dissolving.