the stranger by Albert Camus
http://en.wikipedia.org/wiki/The_Stranger_(novel)
Another great book, I have read it 3 times. While the Plot might seem like just another story the character asks many questions and has doubts about things such as human nature, love and the meaning of life. These days when we had so much talk about what Love is, I rememeber that in the book the character has a woman and she asks him if he loves her.
Since he can't understand or explain 'love' he can't give her an answer. There is one part in the book where the character says something like:
'she said I'm weird and that's why she loves me, maybe, however one day she might not love me for the exact same reason'.