One of the themes might possibly be that in order to survive, camouflage must be used in some sort. Whether it is hiding your feelings, intelligence, or yourself.
this book could also be about courage and will to go on after so much. there is a huge amount of fear invovled in this book.

This book could also be sadness because every time Peekay opens his heart to someone, they either leave him or he leaves them.

To add onto the idea above, I would think that theme would make more sense if rephrased as something like, Being able to share moments of their life with someone happens too quick that being able to leave one another would be just as fast. If someone would like to help with this idea, add more to this theme.

Along with the Peekay Theme, People who you open your heart to may not always be there, and you cant expect them to be, the better you can withstand having your heart torn apart, the more connections you can make, the more people you can rely on and the more friends you will have.