Fritz

I don't think that I can help with your query regarding Fritz' behaviour, Emily, as I don't think that this book gives sufficient insight into the personality and behaviour of its characters. It does paint Fritz as a person of rash and fanciful decisions, (capricious?), so trying to work out what motivated him is rather difficult. Sadly, as you say, the author does not make you care for the characters at all and the main surprise for me is that they are actually based on real people.
I do agree that the updating at the end is the best bit and suddenly makes one take the whole thing more seriously. Sadly, a little too late.
I wonder why the book was written as the author does not seem to care enough about the characters either.