The Home And The World by Rabindranath Tagore
The book is set in early 20th century India in the estate of the rich Bengali noble Nikhil. He lives happily with his beautiful wife Bimala until the appearance of his friend and radical revolutionist, Sandip. Sandip is a passionate and active man, a contradiction to the peace-loving and somewhat passive Nikhil. Bimala finds herself attracted to Sandip creating a love triangle.
Although Nikhil figures out what is happening, he is a mature person and thus grants Bimala freedom to grow and choose what she wants in her life. Meanwhile Bimala experiences the emotions of love for the first time in a manner which helps her understand that it is indeed her husband Nikhil who really loves her.