The Sense of an Ending by Julian Barnes
The premise is fairly simple: three boys meet in grade school and encounter a fourth, a new kid named Adrian, who is cerebral, exceedingly quiet and preternaturally calm. The narrator of The Sense of an Ending is Tony Webster, one of the gang, who is now fully grown and is recounting his young life and how it led him to his present predicament. But that comes later.
Back in the past, no one is surprised when Adrian earns himself a place at Cambridge. He reads philosophy, naturally. But the real conflict begins when Adrian begins dating Veronica, one of Tony’s ex-girlfriends. There is a falling out in which a nasty letter is written, and before Tony and Adrian can patch things up, Adrian commits suicide.
Fast-forward fifty years. Tony has recently retired from the civil service and is living a quiet life as a pensioner in London. Having studied and graduated, married and divorced, Tony wonders if the details of his risk-averse, rather nondescript life have been determined by circumstance rather than by choice; that is, he wonders if his life, always so cautiously lived, is simply something that he passively experienced as it happened to him.
Many years later, Tony discovers that Adrian (now deceased) had willed Tony his diary. Tony believes that it may hold clues to Adrian’s death and may afford him some closure. There’s only one problem: Veronica (Tony’s ex- and Adrian’s erstwhile companion) has possession of the diary and she’s unwilling to part with it. In his attempt to secure the diary, Tony must confront another figure from his past, and face the possibility that his life has betrayed some of his early ideals, as well as the memory of his dead friend.