In 1819, Keats wrote "The Eve of St. Agnes", "La Belle Dame sans Merci", "Hyperion", "Lamia" and a play, Otho the Great (critically damned and not performed until 1950). The poems "Fancy" and "Bards of passion and of mirth" were inspired by the garden of Wentworth Place. In September, very short of money and in despair considering taking up journalism or a post as a ship's surgeon, he approached his publishers with a new book of poems. They were unimpressed with the collection, finding the presented versions of "Lamia" confusing, and describing "St Agnes" as having a "sense of pettish disgust" and "a 'Don Juan' style of mingling up sentiment and sneering" concluding it was "a poem unfit for ladies". The final volume Keats lived to see, Lamia, Isabella, The Eve of St. Agnes, and Other Poems, was eventually published in July 1820. It received greater acclaim than had Endymion or Poems, finding favourable notices in both The Examiner and Edinburgh Review. It would come to be recognised as one of the most important poetic works ever published.
On 3 April 1819, Brawne and her widowed mother moved into the other half of Dilke's Wentworth Place, and Keats and Brawne were able to see each other every day. Keats began to lend Brawne books, such as Dante's Inferno, and they would read together. He gave her the love sonnet "Bright Star" (perhaps revised for her) as a declaration. It was a work in progress which he continued at until the last months of his life, and the poem came to be associated with their relationship. "All his desires were concentrated on Fanny". From this point there is no further documented mention of Isabella Jones. Sometime before the end of June, he arrived at some sort of understanding with Brawne, far from a formal engagement as he still had too little to offer, with no prospects and financial stricture. Keats endured great conflict knowing his expectations as a struggling poet in increasingly hard straits would preclude marriage to Brawne. Their love remained unconsummated; jealousy for his 'star' began to gnaw at him. Darkness, disease and depression surrounded him, reflected in poems such as "The Eve of St. Agnes" and "La Belle Dame sans Merci" where love and death both stalk. "I have two luxuries to brood over in my walks;" he wrote to her, "...your loveliness, and the hour of my death".
He used the term negative capability to discuss the state in which we are "capable of being in uncertainties, Mysteries, doubts without any irritable reaching after fact & reason ...[Being] content with half knowledge" where one trusts in the heart's perceptions. He wrote later: "I am certain of nothing but the holiness of the Heart's affections and the truth of Imagination – What the imagination seizes as Beauty must be truth – whether it existed before or not – for I have the same Idea of all our Passions as of Love they are all in their sublime, creative of essential Beauty" again and again turning to the question of what it means to be a poet. "My Imagination is a Monastery and I am its Monk", Keats notes to Shelley. In September 1819, Keats wrote to Reynolds "How beautiful the season is now – How fine the air. A temperate sharpness about it ... I never lik'd the stubbled fields as much as now – Aye, better than the chilly green of spring. Somehow the stubble plain looks warm – in the same way as some pictures look warm – this struck me so much in my Sunday's walk that I composed upon it". The final stanza of his last great ode, "To Autumn", runs: