fall apart vs split up

fall apart is not a noun while split up is a noun.

Word	Noun	Adjective	Verb	Adverb
fall apart	No	No	Yes	No
split up	Yes	No	Yes	No

As verbs, fall apart and split up are synonyms defined as:

Other synonyms of fall apart include break, come apart, separate.

fall apart (noun)	split up (noun)
	an increase in the number of outstanding shares of a corporation without changing the shareholders' equity

fall apart (verb)	split up (verb)
become separated into pieces or fragments	become separated into pieces or fragments
break or fall apart into fragments	get a divorce; formally terminate a marriage
go to pieces	discontinue an association or relation; go different ways
lose one's emotional or mental composure	separate into parts or portions