What do i do about this irritating coworker

I hate this coworker. I just got more responsibility at work and have to look good for work. However there's this new person who keeps trying to be romantic towards me when I told them already that I'm really not interested. Part of it is they want to fuck around with me to make their partner super jealous. So they keep telling their partner and everyone at work we are dating when we are not. Then they are harassing me because I'm in good standing with a lot of the higher staff who are above my ranking. Saying its probably only have good standing because I snitch on everyone. They won't stop this and I'm scared to report this because then he'll just say "see you are a snitch this is why everyone hates you". I'm really irritated.