Then she was toying with you. She was discovering that her beauty gave her power over men and boys, and you took the bait. There's nothing beautiful about that, it baffles me you fail to see it now that you're grown. You can turn around the bushes and make this experience more than there really was (at the beginning you were implying the two of you had sex and had a kind of friendship). But there was no love, no friendship, no meaningful exchange or sex in this situation, just power-play and obsession.
That's what I quickly suspected when I read your story John.
I've been there as a girl, feeling empowered and confident when you feel admired, desired, etc. by a boy. Luckily for me my empathy would kick in when I would realize that a boy was really "in love" (as a teenager might be) with me and I didn't have the same feelings towards him. It felt wrong and unworthy for me to be the cause of someone's suffering when I could do something to prevent that person from remaining deluded and continuing to suffer.
But, as is often the case, the truth can hurt more (at least in the moment) than an illusion, no matter how difficult it is to live with (the illusion).
At that time, in the beginning, I would approach the boy and say, as tactfully and gently as possible (so as not to hurt their feelings), something like: "I'm sorry if what I'm about to say is going to hurt you, but I think it's much worse to keep you under the illusion that there might be a love affair/story between us. If it's ok with you we can be/remain friend."
Then I realized that too much sweetness and the "if it's ok with you we can be/remain friends" was too much, as it fed the hope in the boy that things could change" and as a result, they kept sticking to me or watching me from afar. So I became a little more direct and less "soft", it could make me come across as harsh or haughty, but it was necessary to break their wishful thinking/feeling and that was the point.
More than once I got the answer, "I wish you hadn't told me, so I could have kept dreaming..."
I've had quite a few friends in the past who have been "fooled" by girls like this, sometimes it's not even conscious on the part of these girls, at that age, or at least not done intentionally to do harm, but as adults if they continue it's because, more often than not, they've moved on to a very conscious power manipulation.
While trying to discuss with them (the male friends) I realized how difficult it is for them to see the truth, how great is the pain to admit that they have been lured and they have been deceived themselves on something that made them so alive, so full of hope and enthusiasm, maybe the only thing that illuminated their life at that moment, the illusion of loving and being loved...