In this English SE discussion, the history of **romance** in literature was covered fairly extensively; and we basically concluded that **romance** originally meant stories or histories styled poetically (i.e. in rhyme or verse) that were subsequently put to music in songs and ballads sung by troubadours, bards, or minstrels -- who were frequently rewarded for their skills with favors from pretty ladies.
(Like modern groupies or really devoted fans of that sort of entertainment.)
In that manner, the idea of love affairs eventually became culturally and socially associated with **romance** (which in medieval times was defined quite simply as _poetry_ ).