Is there any reason why my sister lies about talking to my boyfriend?

My sister keeps talking to my boyfriend and they hang out. He comes to me and tells me what all they did. He even mentioned that they had lunch together one day. Whenever I ask her did she talk to or see my boyfriend today, she says no she doesn’t talk to or see him. My boyfriend is confused and doesn’t understand why she is lying to me.

Is there any reason why my sister lies about talking to my boyfriend?
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