What does this simile mean??

Knowledge of the Secret torments Brian throughout the entire novel, but particularly at the beginning. Chapter 4 is the first time readers learn what this secret actually is: that Brian witnessed his mother cheating on his father while they were still married, kissing an unknown man in a car in the mall parking lot. His time in the forest distanced from his family for long enough to come to terms with the Secret and not let it define his life any longer.

It means it hurts to think of it and it makes you sad