Girlfriend thinks I don't share enough details, what should I do?

I've been with my girlfriend for about one year now and in general our relationship is very good. However, recently she seems to think that I'm not sharing enough about my life with her. I'm really at a loss because I know all of the details that happen in my life and I really don't think I hold back much of it from her.

For example, a bought a book and for some reason on that day our conversation went a certain direction and I didn't get to tell her about it. A few weeks later, she finds out that I've been reading it and gets really upset that I never told her about it... Does that sound reasonable? What should I do?
Girlfriend thinks I don't share enough details, what should I do?
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