It's interesting how after the 1940's Oona always looked older than her age. I've read the books by Patrice Chaplin and Jane Scovell, and if I remember correctly, she didn't start drinking heavily until after Chaplin died. I think living with him must have been a challenge at times.
According to Patrice Chaplin, Oona's drinking began long before Charlie died. In one of the books it mentions Oona locking herself in her bedroom to drink and Charlie pounding on the door. Perhaps she hid it more while he was alive & the children were small. I don't think it was living with Charlie that caused her to drink. Her father and brothers had alcohol and drug problems. Both of her brothers committed suicide. It seems this behaviour ran in the family. Oona somehow managed to survive them all, but she once told a friend that she was suicidal when she met Charlie and that he saved her life.
That makes a lot of sense. I was a theater geek, and read the Gelb's book about Eugene O'Neill many years ago. The entire family were either addicts or alcoholics, so it is actually amazing that Oona was able to create a life for herself. What a heartbreaking saga, though.
It amazes me that Charlie would stay with Oona than if she was already drinking. He had to of known. I mean, he couldn't stand alcoholics so she must have meant so much to him if he stayed. Granted, he was an older man but still.