sharky, you may well be reading too much into this. You say he was well read and fond of books... maybe he just liked Candide as a book and gave it to you as something of himself, that sounds stupid perhaps but I've done that myself. Just before I split from my last serious relationship I gave my GF but The Waves and Frankenstein - for no reason than that these were two of my favourite books and I thought she might be able to share something with me.
However I must say I made it clear to her where our relationship stood.

As personal advice I would say forget the book and move on.

however if he does have some meaning to convey in the book I would suggest that it might be purely related to him, and what he is doing with his life, rather than some sort of comment on you both.