Did you know that to say “each other” we use two words друг and, depending on the case, the second part of this expression is declined? The preposition is put between these two nouns. Logically, the Nominative case of this expression doesn’t exist.G. друг друга
D. друг другу
A. друг друга
I. друг другом
P. друг о друге
Они любили друг друга. They loved each other.
Они заботились друг о друге. They took care of each other.
Они шли друг за другом. They were walking one after another.