Hmmm...would you say the same if it was a 17 year old female and a 37 year old man? This guy is basically a junior in high school. Would you care if a 17 y/o female student was letting her 40 y/o teacher bang her?
If you're gonna go on your own way you cant give a chit about what she thinks anymore. Trust me. The less attention you give the more women will crave you. I dont know why but that's just how it works.
If she wanted you she wouldn't be toying with you. She wants you in the odd sense that she likes the fact that you're gonna chase her like a sad puppy dog. My advice is to go dry on her. Be cordial but act like she doesn't exist.