romance vs love story

romance and love story both are nouns.

Word	Noun	Adjective	Verb	Adverb
romance	Yes	No	Yes	No
love story	Yes	No	No	No

As nouns, romance and love story are synonyms defined as:

romance (noun)	love story (noun)
an exciting and mysterious quality (as of a heroic time or adventure)	a story dealing with love
a novel dealing with idealized events remote from everyday life
a story dealing with love
a relationship between two lovers

romance (verb)	love story (verb)
tell romantic or exaggerated lies
talk or behave amorously, without serious intentions
have a love affair with
make amorous advances towards