How we cite our quotes:
He was still an alcoholic, always would be, probably since Sophomore Class Night in high school when he had taken his first drink. (14.54)
Jack's alcoholism is a major part of his isolation. Even though he's recovering, he thinks about drinking all the time. When he was drinking, it isolated him from his family, his students, and his writing. His temper is the other big isolating factor, and his temper plagues him, drunk or not.
The actual act of writing made her immensely hopeful, not because she expected great things from the play, but because she her husband seemed to be slowly closing a huge door on a room full of monsters. (16.1)
Wendy thinks writing is the key to helping Jack come out of the isolation brought on by his temper, his drinking, but most of all by his childhood of abuse.
"Hello? This is Jack Torrance […]. My son here can't stop crying. Please send THE MEN INWHITE COATS to take him to the SANNY-TARIUM. He's LOST HIS MARBLES." (21.119)
Danny feels very isolated by his ability, especially when he's at the Overlook and he starts to see all sorts of crazy things. He's afraid if he breaks down and shows his torment, he'll be deemed insane and isolated in a psychiatric hospital.