I need help...

I have a a guy friend that I've known for maybe 2 years now he's is younger then me he's 17 and I'm 19 going on 20. He's still a virgin I was his first kiss (just kinda happenes) he's keeps telling me he wants me to be his first. I'm in a relationship that's been going on for a year now. I keep telling him that it should be someone special he keeps telling me your that someone special. So I go on and say the time will come were you'll find someone better that's worth that.

I seriously don't know what to do any more. What do I tell him? How do I get him to drop the subject? Ugh..