Newland Archer, always fell in love with Countess Ellen Olenska, eventhough he’s married to her cousin May Welland.
He almost sacrificed his marriage, and followed Ellen sudden leaving for Europe. May interrupted by saying she was with a child. Newland believed that is the main reason why Ellen left.
Feeling trapped, Newland decided to stay and live his loveless marriage for the sake of their child(ren). He remained faithful to May until her last day. May passed away, caused by pneumonia.
Years years later, Newland had the opportunity to see or perhaps, at the end be with Ellen. But.. he chose to walk away.
Moral of the story : some people are not meant to be together. Not because God wants to. But by choice, IMO. The willingness to sacrifice your own ego and happiness for the sake of others. That’s the noblest thing to do.