These claims about Lucretius' life are not generally now believed, because:
Firstly, the Epicurean philosophy expounded by Lucretius sets great store on reason and discourages romantic attachments.
Secondly, it would have been exceedingly difficult for Lucretius to compose a sustained poetic masterpiece if he were raving mad most of the time. As Cicero remarked to his brother Quintus in a letter, "The poems of Lucretius contain, as you say in your letter, many flashes of inspiration and also much poetic skill."
It is likely that Jerome, as one of the early church fathers, would have wanted to discredit Lucretius' philosophy, which includes disbelief in any kind of life after death and in any divinity concerned with man's welfare. This defamation involved ad hominen attacks imputing immorality, the use of witchcraft and insanity to the poet.
Finally, Virgil writes in the second book of his Georgics, clearly referencing Lucretius, "Happy is he who has discovered the causes of things and has cast beneath his feet all fears, unavoidable fate, and the din of the devouring Underworld" As M.F. Smith argues in his introduction to the Loeb edition of the poem, Virgil would have been a heartless sarcastic cynic to write such sublime lines about a man who had in fact taken his life in deranged depression. (John Goodwin)
Cicero implies in one of his letters to his brother that they had once read Lucretius' poem. This is the last mention of Lucretius until Aelius Donatus, in his Life of Virgil, while stating that Virgil assumed the toga virilis on October 15, 55 BC, adds "it happened on that very day Lucretius the poet died." If Jerome is accurate about Lucretius' age (44) when he died, then based on other evidence that confirms 55 BC as Lucretius' year of death we can then conclude he was born in 99 BC. Also, the work has several allusions to the tumultuous state of political affairs in Rome and its civil strife.
However, the only certain fact of Lucretius' life is that he was either a friend or a client of Gaius Memmius, to whom he dedicated De Rerum Natura. This poem is also thought to be unfinished, although Jerome says that Cicero "amended" it — which may mean he edited it for its eventual publication.
^ John Goodwin in the Introduction of the Penguin Classics De Rerum Natura
Lucretius. De Rerum Natura. (3 vols. Latin text Books I-VI. Comprehensive commentary by Cyril Bailey), Oxford University Press 1947.
On the Nature of Things, (1951 verse translation by R. E. Latham), introduction and notes by John Godwin, Penguin revised edition 1994, ISBN 0-14-044610-9
Lucretius (1971). De Rerum Natura Book III. (Latin version of Book III only– 37 pp., with extensive commentary by E. J. Kenney– 171 pp.), Cambridge University Press corrected reprint 1984. ISBN 0-521-29177-1