Co worker

I've noticed this recently that he's always staring or watching me, sometimes pats me on the shoulder or back and sometimes when I talk to him he just smiles and doesn't say much. I'm much much younger than he is, and the other day I heard him talk about me to someone as I walked past saying that 'she knows but she won't catch on' pretty loudly so I could hear which I thought was abit weird but yeah it's weird as he's always staring or looking at me, he's married too which makes it creepy and wrong. Also caught him licking his lips when he was around me hmm, and when i catch him staring we lock eyes then i quickly look away because its uncomfortable. can anyone relate?