C.S. Lewis’s book presenting affection, friendship, eros, and charity is The Four Loves.
The Four Loves was published in 1960 and develops ideas Lewis had first explored in a BBC radio broadcast series. The book examines four Greek terms and related experiences: storge, or affection; philia, or friendship; eros, or romantic love; and agape, associated with charity or self-giving love.
Lewis does not present the categories as completely isolated boxes. He considers how natural forms of love can be valuable while also becoming possessive or distorted when treated as ultimate. He contrasts these human loves with divine love.
The book is sometimes confused with Lewis’s literary study The Allegory of Love, which examines medieval literature rather than classifying forms of personal love. The Four Loves belongs to Lewis’s popular Christian nonfiction.