Does this cross the student teacher border?

I think things have gotten to the point where you should be concerned. It may be harmless flirting on his part. And he is young and was your age not that long ago. So it may be hard for him to see you and the teenage girl that you are. You need to distance yourself from the alone time that has been happening. You need to find someone that is close to you to talk to. I think it is very normal for him to be attracted to you, but he is the grown up and needs to act like it. And a teacher in a position of authority. OH BTW if he says anything like the "want to screw" thing again tell him how what he is saying is affecting you. That he needs to act his age and look at yours.