How much do you know about manic depression (bipolarity)? You may find that exploring the Mental Health Issues forum section is helpful.
I can personally recommend the book "
When Madness Comes Home: Help and Hope for Families of the Mentally Ill" by Victoria Secunda. It gives a basic overview of the illness but focuses mostly on how the family is affected. Not too technical, with many stories and anecdotes and examples of how others dealt with the situation, including the choice not to deal with it and walk away. Also gives many different points of view from various family member perspectives: parents, spouses, siblings, children etc.
Here is a more comprehensive list of possible further reading.