For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
This lasts from the everything's fine-and-dandy beginning (riches! engagement announcements! high society!) to the serious point of no return when Newland Archer falls in love with Madame Olenska, even though she is his fiancée's cousin. Oops. And Ellen Olenska hearts Newland back. Double oops.
Act II
Both Newland and Ellen are unwilling to break May's heart and scandalize the family, so Newland marries May. Good job, Newland. Way to live that dream. He's comfortably numb for a while, and almost forgets about Ellen, but then he sees her again and all his feelings start up. He wants to leave his wife for her. Barring that, he'll settle for one night alone with her. It looks like their love will be consummated, but then there's radio silence from Ellen Olenska. Newland is bummed.
Act III
Ellen leaves for Europe again. She is polite but chilly toward Newland at her going-away dinner. May tells Newland that she is pregnant, and they go on to raise three children and live a life of quiet desperation. May dies years later, and Newland goes to Paris with his son. He has an opportunity to see Ellen Olenska again, but doesn't take it. YOLO is not Newland’s style.