Should a boyfriend read his girlfriends diary?

IF she hands it to him or says you can, otherwise it's more person than opening the bathroom door on her while a room full of people she doesn't know are standing outside the door. That's her heart and soul- if you are worthy she will share. Elsewise - don't touch it much less read it.

Another analogy. Imagine someone could read your thoughts, all the time, you couldn't hide anything. Most people hate the idea - they are ashamed of some of their thoughts and some are just too painful to share. That book is her mind on paper, treat it as such.