Books or poems or plays with a theme of isolation

Room by Carol Ann Duffy is a poem with a theme of isolation, as is The Windows, arguably. You could perhaps argue that The Windows is a kind of self-imposed isolation depending on what way you interpret it; it's got quite a harsh, passive aggressive tone to it, that's almost resentful, so you might say that the speaker's tone is representative of them being a social pariah almost. Whatever floats your boat.

You could say that The Outsider (L'Étranger) by Albert Camus has a theme of isolation, by way of Meursault (the main protagonist) being alone in his thought processes; refusing to mourn his mother's death as he doesn't feel he needs to. He's essentially a stranger to the usual human reactions to topics such as death, love and injury, etc. He also rejects any help from the Chaplin who comes to visit him in jail, so you could say he's essentially digging his own grave further and further into isolation. His lover/fiancée eventually stops coming into contact with him, as does his best friend. Those close to Meursault and his mother begin to fabricate the truth when talking about him, etc. So this fabrication of the truth maybe could be interpreted as bullying? If you want to stretch it that far.

I haven't read it, but there's also a novel by Emma Donoghue called Room. I'm guessing that has isolation in there somewhere from what I've heard. Brie Larson is supposed to be amazing in the movie, too.