Relationship Advice

I need help ASAP!!! I'm currently talking (occasionally having sex) with this guy that I met in college. When everything started he was a sweetheart and we used to hang out regularly. Now things have changed a bit, I don't see him like I used to when we started talking. He never asked me to be his girlfriend so I have no idea where this "relationship" stands. I'm really into him, and would love to make it official but I don't think we are on the same page. Do you all think he just using me to have sex? ....Help please!!