The Age of Innocence Book II (PDF)

gasp!—separated from her husband, causes a stir in New York society and turns Newland Archer's world upside down. It does not turn his frown upside down, however. Countess Olenska settles in a bohemian neighborhood and leads an unconventional lifestyle. Remember that unconventional in 1870s New York essentially means she eats her fish course with a salad fork. Serious faux-pas.
Over the course of the next few weeks, Newland finds himself having the hots for Countess Olenska. In an effort to get over his attraction to her, he flees to the Wellands's vacation home in St. Augustine, Florida, to persuade May to speed up their wedding date. Cool strategy, bro. But when he returns to New York he finds himself unable to get over Madame Olenska.
He tells her he like-likes her, but she rejects his advances. This isn't because she doesn't like-like him back, though. She thinks that running off with her cousin’s fiancé would be a scumbag move, and Little Old New York has a thing against scumbagginess.
Part I ends as both Madame Olenska and Newland Archer receive telegrams from May, announcing the "happy" news that her parents have agreed to a drastically shortened engagement period. Cue a collective forced smile.
Part II takes up the story again in April. Newland and May are married (booooo) and they leave immediately for a honeymoon in Europe. They tour Switzerland and France and end their trip in London. Newland wants to take in the art and culture and expand his mind, man, but May is mostly concerned with fashion and shopping. Newland thinks, "Huh. We don't seem to have much in common," but keeps that thought to himself.
When they return, they settle into married life, and Newland has no contact with Madame Olenska, who has moved to Washington, DC. But that summer, while on vacation in Newport, Rhode Island, Newland sees Madame Olenska again and his eyeballs turn into cartoon hearts. He tracks her down in Boston, where they talk about how they love each other but can't do a dang thing about it. Longing glances are exchanged. Saxophone music is probably playing in the background.
On Newland's return to New York, there is a crash on Wall Street, and Madame Olenska returns to New York to take care of her grandmother. Newland and Madame Olenska finally decide to consummate their love by having a passionate night of knocking boots before she leaves New York for good.
But before they meet again, Madame Olenska ghosts and abruptly leaves for Washington, DC. A week later, May hosts a farewell dinner for Madame Olenska, who is now leaving for Paris. Newland is bummed. Womp womp. That night, Archer attempts to tell May about his feelings for Madame Olenska, but she tells him that she's pregnant. Not only that, but May told Madame Olenska that she was pregnant a couple weeks before. This explains why Newland and Madame Olenska never got to get it on — Madame Olenska wasn’t cool with sleeping with the hubby of a preggo woman.
The novel ends twenty-six years later. Newland and May have had three children, all grown up, and May has recently died. They've had a pleasant dull life. Newland’s son Dallas invites him to go to Europe with him. In Paris Dallas accepts an invitation for a father-son date at Madame Olenska's. When they arrive at her home, Newland decides not to join his son at Madame Olenska's and returns to the hotel without having seen her.