This is a thorough research into loneliness. As they point out that not everyone that is alone suffers from loneliness. Some people have a smaller threshold for what they consider loneliness.
From apes to humans to many other social animals this book covers what loneliness can do. When you suffer loneliness long term it can affect your brain. You will have slower cognitive recognition. They discuss the many studies they pulled on people to see what being lonely can really do. Study after study proved that if you are lonely you will have certain characteristics which will make you less likeable. which in turns leads to more loneliness.
This book consists of 90% of how suffering from loneliness will screw you up and 10% how to try to break the cycle of loneliness.