I'm not going to let my girlfriend read my journal. What do you think about that?
Why would you keep your journal away from your girlfriend?
I don't need her spending time reading my stuff, she would not understand some of it..
You deserve the right to privacy from your girlfriend and the ability to share sensitive information on you terms.   Make sure that you are avoiding keeping secrets that could damage the relationship.
She won' t understand it anyway, so why bother.
It's your journal and your life. She shouldn't be reading it anyway.