breakup vs splitsville

breakup and splitsville both are nouns.

Word	Noun	Adjective	Verb	Adverb
breakup	Yes	No	No	No
splitsville	Yes	No	No	No

As nouns, splitsville is a hyponym of breakup; that is, splitsville is a word with a more specific, narrower meaning than breakup:

breakup: the termination or disintegration of a relationship (between persons or nations)
splitsville: separation or breakup or divorce

Other hyponyms of breakup include annulment, invalidation.

breakup (noun)	splitsville (noun)
the termination or disintegration of a relationship (between persons or nations)	separation or breakup or divorce
coming apart