incessantly vs forever

incessantly and forever both are adverbs.

Word	Noun	Adjective	Verb	Adverb
incessantly	No	No	No	Yes
forever	No	No	No	Yes

As adverbs, incessantly and forever are synonyms defined as:

Other synonyms of incessantly include always, constantly, perpetually.

incessantly (adverb)	forever (adverb)
invariably	for a limitless time
with unflagging resolve	for a very long or seemingly endless time
	invariably