How to tell a guy you don't like him anymore?

I got myself in a can of worms. I had a small crush on my coworker. My feelings for him changed when we started flirting. In the moment, I would just have fun with it, but later after putting thought into it, realized I don't really like it. It seems sex is always on his mind and he has a young class clown vibe to him at 34. He seems to have been out of the dating game for a while so I don't know if he intentionally doing this sexual flirting or if he thinks that what I want from him. He's always asking if I miss him. Most of his questions tend to lean towards what I feel about him. I don't know if this is out of insecurities or cockiness. Either way, it makes everything feel one-sided. I been wanting to talk to him about it. Or should I just give him the cold shoulder?