How to nicely reject a coworker?

I've been working at a new job for almost a month. There's this male co-worker who likes me and has made it obvious to me and several other coworkers that he does. He doesn't seem to care that I'm not single, wear an engagement ring, and have kids. He's also the type that I think would get aggressive if I try to just ignore him. My fiance thinks it's funny and said that I'm a hot milf that just attracts men. I'm not that attractive and I'm more of a quiet, nerdy person. I can't afford to quit my job since I'm the only one working right now to support our family of 4. How do I reject him nicely?

How to nicely reject a coworker?
Post Opinion