Why does he stare at me if he has a girlfriend?

Theres this guy at my school and he looks at me all the time. He looks at me so much i would’nt of even noticed him if he did’nt look at me as much as he does, i even catch his eyes a couple of times and he never looks away. So just the other day i acknowledged him and said hi and he looked at me real quick and said hi and he has a light nice not deep. I said how are you and he said fine and he looked at me really quick i said whats your name and he did’nt pause to tell me so i asked him did he have a girlfriend and he said yea and had his head down and didnt even want to look at me! so i said stop sign and walked away (because i am not getting beat up for him!) and then i am about to walk out the door and i turn around and hes staring at me again! and i was thinking to myself he just told me he had a girlfriend hes been staring not looking at me ever since august when school started! I don’t know what to do or say i mean i think hes cute but i would of thought he would of said something else but instead he sounds really nonchalant and he only looked at me for about 2 seconds before he looked away but usually we would meet eyes for like 5 seconds if i was not talking to him and i was very shy but i talked to him anyways because i just wanted to know if he would like to do much more than just stare at me everyday. Im confused now.