Why does my girlfriend want to know what I'm up to but don't like me asking her back?

My girlfriend is either texting or asks me face to face what I'm up to or what have I been up to by text. When I've asked her back she won't say and becomes hard of hearing haha. If I dont reply she becomes suspicious.
Why does my girlfriend want to know what I'm up to but don't like me asking her back?
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