zueinander
to each other
Expresses a mutual relationship, action, or movement; one to the other.
Nach dem Streit haben sie nur langsam wieder zueinander gefunden.
After the argument, they only slowly found their way back to each other.

to each other
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to each other
Expresses a mutual relationship, action, or movement; one to the other.
Nach dem Streit haben sie nur langsam wieder zueinander gefunden.
After the argument, they only slowly found their way back to each other.

'Zueinander' (to each other) is a pronominal adverb made up of the preposition 'zu' (to) and the reciprocal pronoun 'einander' (each other). It literally means 'zu einander' (to one another) or 'einer zum anderen' (one to the other).
Seid bitte nett zueinander!
Please be nice to each other!
The word 'zueinander' (to each other) always describes a mutual (reciprocal) relationship. Therefore, it requires a plural subject or a subject that represents a group of at least two people or things.
Die beiden Teams verhielten sich fair zueinander.
The two teams behaved fairly toward each other.
A very common expression is 'zueinander passen' (to go well together / to be compatible). It is used to describe that things, such as colors or clothing, or even people, harmonize well.
Ich finde, das blaue Hemd und die graue Hose passen gut zueinander.
I think the blue shirt and the gray pants go well with each other.
together
'zusammen' and 'zueinander' both have to do with multiple people or things. 'zusammen' says that people do something together or are in one place as a group. 'zueinander' emphasizes the relationship or direction between two or more sides: one to the other. It is especially common with verbs like 'passen', 'kommen', 'stehen', or 'finden'. Learners confuse the words because both can express closeness. A practical rule is: 'zusammen' describes doing something together, while 'zueinander' describes the relationship between the people or things involved.

Die neuen Nachbarn sind freundlich zueinander.
The new neighbors are friendly to each other.
Bei der Arbeit essen wir oft zusammen in der Pause.
At work, we often eat together during our break.