I like the way you’ve spun it. Just giving a flip to the other side gave a full picture. Must admit your version sounds as real as her own. One person in love with the thought of being in love and having a soulmate. Totally oblivious that the other person is seeing through her eyes she is not ‘the one’.
I wish he told her it would not work. I wish he had hurt her up front and broke her heart, so she could grieve and maybe get over him in a few years. ( If she’s as psycho as you it might take medical intervention). Sometimes the kindest thing you can do is to not give hope of a relationship or any benefits. So you both can either gain a respectful parting or become the people who end up hating each other :-)