How should I proceed with this guy at work?

There is this guy at work whom I have a hot and cold work relationship with. He sort of makes it a little difficult to work with. I made the work relationship with him more distant after he insults me for doing my job, that he thought was causing him to stay longer at work. Anyway, I jotice he’s been staring at me lately and trying to get me to talk to him by inserting himself in my conversations or asking me random that he pretends to be work related. Whenever he passes me by he bumps into me unecessarily, even if I avoid hi. Or he touches me back for leverage to pass by. He talks about his girlfriend contantly with costumers. She is a great girl and is sister to another coworker. But he has been singing love songs around me when the come on the radio. Songs like, “I fooled around and fell in love”, “I’m in over my head”, or anything that some guy is singing about some girl and he just stays near me amd sings out. He keeps telling me goobye when he is leaving work even after I have not been replying to him day after day. Why would someone behave like this? Is he being unprofessional?