Biographers of the Brontës have generally guessed that the addressee was William Weightman, who was curate at Haworth from 1839 until he died of cholera in 1842.
This identification is purely speculative, but there does not seem to be a better candidate. Weightman is handsome, if not perhaps “angel fair”, in a pencil sketch by Charlotte.
He had a reputation for flirting with women:
I dare say you have received a valentine this year from our bonny-faced friend the curate of Haworth. I got a precious specimen a few days before I left home, but I knew better how to treat it than I did those we received a year ago. I am up to the dodges and artifices of his lordship's character. He knows I know him, and you cannot conceive how quiet and respectful he has long been. Mind I am not writing against him—I never will do that. I like him very much. I honour and admire his generous, open disposition, and sweet temper—but for all the tricks, wiles, and insincerities of love, the gentleman has not his match for twenty miles round. He would fain persuade every woman under thirty whom he sees that he is desperately in love with her.
Charlotte Brontë (3rd March 1841). Letter to Ellen Nussey. In Clement Shorter, ed. (1908). The Brontës: Life and Letters, pp. 204–206. New York: Charles Scribner.
Charlotte mentions that she caught him looking at Anne in church:
‘His young reverence,’ as you tenderly call him, is looking delicate and pale; poor thing, don’t you pity him? I do from my heart! When he is well, and fat and jovial, I never think of him, but when anything ails him I am always sorry. He sits opposite to Anne at church, sighing softly, and looking out of the comers of his eyes to win her attention, and Anne is so quiet, her look so downcast, they are a picture.
Charlotte Brontë (30th January 1842). Letter to Ellen Nussey. In Life and Letters, p. 228.
He was known for his kindness to his parishioners:
There is one little trait respecting him [Weightman] which lately came to my knowledge, which gives a glimpse of the better side of his character. Last Saturday night he had been sitting an hour in the parlour with papa; and, as he went away, I heard papa say to him—‘What is the matter with you? You seem in very low spirits to-night?’ ‘Oh, I don't know. I’ve been to see a poor young girl, who, I’m afraid, is dying.’ ‘Indeed, what is her name?’ ‘Susan Bland, the daughter of John Bland, the Superintendent.’ Now Susan Bland is my oldest and best scholar in the Sunday-school; and, when I heard that, I thought I would go as soon as I could to see her. I did go on Monday afternoon, and found her very ill and weak, and seemingly far on her way to that bourne whence no traveller returns. After sitting with her some time, I happened to ask her mother if she thought a little port wine would do her good. She replied that the doctor had recommended it, and that when Mr. Weightman was last there he had sent them a bottle of wine and a jar of preserves. She added that he was always good to poor folks, and seemed to have a deal of feeling and kind-heartedness about him. This proves that he is not all selfishness and vanity. No doubt there are defects in his character, but there are also good qualities. God bless him!
Charlotte Brontë (29th September 1840). Letter to Ellen Nussey. In Life and Letters, pp. 192–193.
When he died, a subscription was made to erect a memorial tablet placed in the north aisle of Haworth Old Church, reading:
He was three years curate of Haworth, and by the congregation, and parishioners in general, was greatly respected, for his orthodox principles, active zeal, moral habits, learning, mildness, and affability: his useful labours will long be gratefully remembered, by the members of the congregation; and Sunday school teachers, and scholars.
On these slender foundations biographers have built a superstructure of speculation:
In Agnes Grey, the curate whom Agnes marries is a Mr. Weston, and he is said to have been based on William Weightman. A poem written by Anne Brontë is considered to have been an expression of her feelings at the death of the young curate, for during her lifetime, Mr. Weightman was the only curate with whom she was closely associated.
Ellis H. Chadwick (1914). In the Footsteps of the Brontës, pp. 165–167. London: Isaac Pitman.