The Lady of the Camellias

The theme of The Lady of the Camellias is a love story between Marguerite Gautier, a "demi-mondaine" ("courtisane" in the original French, i.e., a woman "kept" by various lovers, frequently more than one at a time) suffering from tuberculosis, and a young provincial bourgeois, Armand Duval. The narration of the love story is told by Duval himself to the (unnamed) narrator of the book. She is named as the Lady of the Camellias because she wears a white camellia when she is available to her lover(s) and a red one when her delicate condition precludes making love. Armand falls in love with Marguerite and ultimately becomes her lover, convincing her to turn her back on her life as a "courtisane" and live with him in the countryside.
This idyllic existence is broken by Armand's father, who, concerned by the scandal created by the illicit relationship and fearful that it will destroy his daughter's (Armand's sister's) chances of marriage, convinces Marguerite to leave Armand, who believes, up until Marguerite's death, that she has left him for another man. Marguerite's death is described as an unending agony, during which Marguerite, abandoned by everyone, can only regret what might have been.
(Source: Wikipedia)