fall in vs get together

fall in is not a noun while get together is a noun.

Word	Noun	Adjective	Verb	Adverb
fall in	No	No	Yes	No
get together	Yes	No	Yes	No

As verbs, fall in and get together are synonyms defined as:

fall in and get together: become part of; become a member of a group or organization

Other synonyms of fall in include join.

fall in (noun)	get together (noun)
	a small informal social gathering

fall in (verb)	get together (verb)
break down, literally or metaphorically	get together socially or for a specific purpose
become part of; become a member of a group or organization	become part of; become a member of a group or organization
to take one's place in a military formation or line	get people together