marriage vs spousal relationship

marriage and spousal relationship both are nouns.

Word	Noun	Adjective	Verb	Adverb
marriage	Yes	No	No	No
spousal relationship	Yes	No	No	No

As nouns, marriage and spousal relationship are synonyms defined as:

marriage and spousal relationship: the state of being a married couple voluntarily joined for life (or until divorce)

Other synonyms of marriage include matrimony, union, wedlock.

marriage (noun)	spousal relationship (noun)
the act of marrying; the nuptial ceremony	the state of being a married couple voluntarily joined for life (or until divorce)
two people who are married to each other
the state of being a married couple voluntarily joined for life (or until divorce)
a close and intimate union