It was books that made me feel that perhaps I was not completely alone. They could be honest with me, and I with them.

This quote is referring to the feeling of comfort and connection that one can experience in reading books. Books can be seen as friendly and supportive to someone who feels isolated in life. They can provide an understanding of the world for which one can offer self-expression and honesty in return. Reading books can offer comfort and companionship to someone who feels alone, as if the author and the reader understand each other.