It is not at all surprising that Ruth kept her past to herself. She had plenty to want to forget, of course, and it would have served no good purpose to share that kind of ugliness with her young children. She was also busy just trying to provide all the best opportunities for her many children (as well as enduring the grief of loss--many times over) and could not afford to dwell on things which did not promote that cause. While telling her children about her past might have explained many things to them, it certainly was not going to put food on the table, pay tuition, or provide for them in any way.
She kept it secret for the same reasons all of us keep our painful pasts secret: it hurt. Divorce, separation, rape, etc. are all painful realities of so many people's lives. In the case of Ruth, she knew eventually she would have to talk about it since she had James. James, like any inquisitive and intelligent child, was bound to ask questions as soon as he realized his life did not mirror the lives of his friends at school. She hoped, no doubt, that the questions would come later rather than sooner, and when they did, she found that talking about her past acutally made her feel better...not worse as she anticipated.
Ruth, the mother of the James McBride, the narrator in this book, most likely kept her past secretive because much of it was very painful and she did not want to rehash it. She had tried to block it out of her mind and push it far away, into the "corners" of her mind, but Mr. McBride was finally able to get it out of her later in her life in order to write his book. Ruth had endured a difficult life and she had to concentrate on her children because both of her husbands passed away and she had to support all of them. Whenever Mr. McBride, in his childhood and adolescence, tried to speak wih her about it, she would immediately refuse to do so and would get irritated with him. It was a very painful subject for her. Once she agreed to talk with him about it later in her life, she found it therapeutic.
Mr. McBride came to the college where I teach last year to speak (and he also played with his jazz band!) about this book and he was marvelous--extremely intelligent, knowledgeable and gracious. If you ever get to go see him speak and talk about this book, do so!
To learn more about Mr. McBride, check out his website at www.jamesmcbride.com. It's really cool!