In the dystopian fantasy world presented to us by Ayn Rand in Anthem, everyone is expected to love everyone else, to regard everyone as a friend. It is therefore considered a great social evil, as well as being illegal, for someone to choose their own friends.
This constitutes what is called the Transgression of Preference, which according to the state involves loving someone better than everyone else. And in this radically egalitarian society, that's a very serious crime.
And yet the narrator of the story, Equality 7-2521, has violated the law by choosing International 4-8818 as his friend. The narrator openly admits that this is an evil thing to say—at least according to the warped standards set down by the state—which explains why he and his friend have never spoken about it.
And yet they know they are friends. They know it when they look into each other's eyes. They also come to know other things, strange things for which there are no words and which frighten them.
The state may be able to control people's words, but it cannot control their emotions; it cannot control how people feel about each other. It can certainly impose universal friendship, but it cannot give such friendship true depth and meaning. Only people can do that when they form friendships entirely of their own volition.