幾久しく: forever

continue

for many years

久しい: long, a long time since

(formal) Female third-person singular pronoun; she, her, girlfriend

(colloquial) a girlfriend (a female partner in a romantic relationship)

年久しく: for many years

(literary) they (about women or girls)

久しく: for a long time

he / distal demonstrative, something far off removed from both speaker and listener: that / boyfriend