Is he just using me for . ?

I have a guy friend who is always trying to have some type of ual contact with me. I mean I didn't mind when he was just touching or me but now it's like he really wants to have with me. When I first told him no I told him it was because we weren't close enough so he began talking to me a lot more. I was kinda persuaded but not enough. Whenever the time comes to do anything he becomes really sweet and nice to me, which he normally isn't, I gave in to a few things because of this but not sex. And if we aren't doing anything sexual it's not like he's mean or anything but it's just not the same. He knows I have liked him for years and that's why I think he's using me. Plus he has a girlfriend, who he never asks to do anything with. Do you all think he's just using me for sex?