I'm glad you found the material I posted to be useful. I've reposted
it below, with a bit of additional information.
To say that something or someone is "the bane of my existence" means
that the person or thing is a constant irritant or source of misery.
As a cliché, "bane of my existence" has lost its edge to a large
degree over the years, and today is most often applied to something
that may profoundly annoy us but is certainly bearable... "Bane of my
existence" is now almost always used in a semi-jocular, "what are you
gonna do?" sense.
But "bane" was once a very serious word. The Old English "bana" meant
literally "slayer" in the sense we now use "killer" or "murderer."
Early on, the English "bane" was also used in the more general sense
of "cause of death," and by the 14th century "bane" was used in the
specialized sense of "poison," a sense which lives on in the names of
various poisonous plants such as "henbane" and "wolfbane."
From this very literal "something that kills you" usage, "bane" by the
16th century had broadened into its modern meaning of "something that
makes life unpleasant, a curse."
A bit more on the word "bane":
O.E. bana "slayer, murderer," from P.Gmc. *banon, cognate with *banja-
"wound" (cf. O.Fris. bona "murderer," O.H.G. bana "murder," Goth.
banja "stroke, wound"), from PIE base *bhen- "to strike, wound" (cf.
Avestan banta "ill"). Modern sense of "that which causes ruin or woe"
is from 1577.
Online Etymology Dictionary
My Google search strategy:
Google Web Search: origin "bane of my existence"