One of the best books on mental illness that I've read in a long time is "Loving Someone with Borderline Personality Disorder." Getting a diagnosis of Borderline Personality Disorder used to be a terrible experience, because it was said that it was basically untreatable. Today, thanks to dialectical behavior therapy (DBT) and better use of medications, people with Borderline have an opportunity to function at a much better level.
Author Shari Y. Manning, whose practice focuses on people with Borderline, has some wonderful advice in the book. Her definition of the disorder is slightly different from the classical definitions I've heard. It is focused on emotional dysfunction, as well as tendency to self-harm, problems with impulse control and difficulties to managing relationships.
That actually makes the tips in the book even more helpful as they focus on dealing with a person who has out-of-control emotions. The subtitle is actually "How to Keep Out-of-Control Emotions from Destroying Your Relationship." Dealing with very intense emotion is a frequent problem when you love someone with bipolar disorder, as well. Manning's tips are helpful, as is her explanation of the difference between self-harm and suicidal thoughts.
It's good book with good ideas for controlling your own emotions and soothing yourself before you get sucked into an emotional storm.