sexual activity vs unfaithful

sexual activity is a noun but unfaithful is not a noun.

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

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

sexual activity (adjective)	unfaithful (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