unfaithful vs sex activity

unfaithful is not a noun while sex activity is a noun.

Word	Noun	Adjective	Verb	Adverb
unfaithful	No	Yes	No	No
sex activity	Yes	No	No	No

unfaithful (noun)	sex activity (noun)
	activities associated with sexual intercourse

unfaithful (adjective)	sex activity (adjective)
not true to duty or obligation or promises
having sexual relations with someone other than your husband or wife, or your boyfriend or girlfriend
having the character of, or characteristic of, a traitor
not trustworthy