What is the origin and meaning of the phrase “bane of my existence”?

"Bane" is a somewhat archaic word implying that the thing being described is good for killing (or at least getting rid of) something else. For example, wolfsbane is a plant that was traditionally used to poison wolves.

The earliest use I found of the phrase is in Arthur Neil's Adelaide: An Original East Indian Story, published in the September 1794 edition of The Sentimental and masonic magazine (v.5, page 206):

Lindsey, from his earliest acquaintance with Miss Pomeroy, had been the bane of her existence ; the small degree of affection her father had hitherto shewn, he had alienated from her ; and he, she doubted not, it was, who had spread the groundless calumny that harried her from France ; he, too, now with persevering cruelty, though though the Governor frequently heard from Ireland, and though Lady Catherine often wrote to her, and expressed, in every letter, the utmost astonishment at receiving no reply, even this first wish of Adelaide's heart he artfully contrived she should not be gratified in, well knowing, from Belmour's attachment, if made acquainted with the truth of her situation, that Adelaide would not long remain subject to his power, so much did the tenure of Mr. Pomeroy's many very lucrative posts depend on the pleasure of the Earl, and so much was the Governor dazzled by the splendor of Lindsey't alliance, that, at his instance, he consigned to the flames, unperused, all Lady Catherine's letters to his daughter, persuaded that the less indulgence she found in her confinement, the more speedily she would consent to their wishes.

(This single sentence has 1,158 characters, 190 words, 27 commas and three semicolons.)

Found this online; sounds like Bane may have been the source of pain for Scots and others.

Donald Bane, also spelled Donaldbane, or Donalbane, Bane also spelled Ban or Bain (born c. 1033—died after 1097), king of Scotland from November 1093 to May 1094 and from November 1094 to October 1097, son of Duncan I.

Upon the death of his brother Malcolm III Canmore (1093) there was a fierce contest for the crown. Donald Bane besieged Edinburgh Castle, took it, and, with the support of the Celtic Scots and the custom of tanistry (the Celtic system of electing kings or chiefs), he was king nominally for at least six months. He was expelled by Duncan II, son of Malcolm, assisted by English and Normans and some Saxons. Duncan’s reign was equally short, for Donald Bane had his nephew slain and again reigned for three years.

These years saw the last attempt of the Celts to maintain a king of their race and a kingdom governed according to their customs. Edgar the Aetheling, who had newly befriended the Norman king of England, led an army into Scotland, dispossessed Donald Bane, and advanced his nephew Edgar, son of Malcolm III, as sole king of the Scots