On Wednesday 13 October 1819 Keats wrote to Fanny Brawne:
My dearest Girl,
This moment I have set myself to copy some verses out fair. I cannot proceed with any degree of content. I must write you a line or two and see if that will assist in dismissing you from my Mind for ever so short a time. Upon my Soul I can think of nothing else. The time is passed when I had power to advise and warn you against the unpromising morning of my Life. My love has made me selfish. I cannot exist without you. I am forgetful of everything 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—I should be exquisitely miserable without the hope of soon seeing you. I should be afraid to separate myself far from you. My sweet Fanny, will your heart never change? My love, will it? I have no limit now to my love…
Do not threat me even in jest. I have been astonished that Men could die Martyrs for religion—I have shudder’d at it. I shudder no more—I could be martyr’d for my religion—Love is my religion—I could die for that. I could die for you. My Creed is Love and you are its only tenet. You have ravish’d me away by a Power I cannot resist: and yet I could resist till I saw you; and even since I have seen you I have endeavoured often “to reason against the reasons of my Love.” I can do that no more—the pain would be too great. My love is selfish. I cannot breathe without you.
Yours for ever John Keats