Why is my senior pretending to be single and spreading rumors about us?

This senior in my office is spreading information that he is right now single when he clearly has a girlfriend in real life. Upon that he is slowly spreading rumors like Me and he are seeing each other. He is getting supported by other seniors. But why lie?
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The senior has invited me to a party... and I am confused whether I should go or not.
Why is my senior pretending to be single and spreading rumors about us?
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