Why is this guy not listening to me when I say no?

There's this guy at work and his desk in next to mine.

I have no interest in him and I've told him no so many times when he asks me to do stuff with him

First he started asking me for coffee, then lunch,. to come and have a drink just me and him. I've said no all these times.

Then last Sunday he messaged me on Facebook at 2am asking me to come over to his place.

We. got along well at first but now he's making me. feel uncomfortable and I've been here 6 months and don't want to get in a work relationship anyway.

I've told him no nicely all these times but I can't hold it in and feel like next time he asks I'm going to tell to f off and I can't do that at work.

I feel uncomfortable sitting next to him and want to move desks.

Should I tell someone at work?

Why is this guy not listening to me when I say no?
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