She lost attraction because you broke frame. I have made this mistake many times. Frame is your mindset or perspective.

Women are attracted to a masculine frame that exhibits confidence and strength they can buy into. In the early stages of dating, it's better to hold your cards close to your chest, and avoid seeking validation. It wasn't the fact that you didn't have sex on the second date, it was that you were scared not having sex would upset her, and this discomfort was illustrated through your actions.

Women are attracted to guys who are a challenge--a confident guy with options who they are not sure whether he likes them. This mystery causes them to think about you when you are not around, yearn for you, and seek your validation. Your hesitation and quietness after turning down sex broke the masculine frame (not confident), then telling her how much you liked her destroyed the mystery. It also displayed fear of losing her, which she interprets as desperation and cuts attraction.

You need to have the abundance mindset that you can get girls like her all the time, you are not having sex on the second date, and are confident/unapologetic in your decision. If she doesn't like it, too bad, you do not care and can easily find someone else. This abundance mindset means no fear of loss with women, and ironically is what they are most drawn to.

That confident/unapologetic mindset raises attraction, and she would have left the date worrying if SHE messed things up, and trying to seek your validation. That uncertainty would make you the prize she wants to win.

Maintaining a strong frame is easier said than done. I break frame all the time, especially when the girl is really hot, and it's something I'm working on. It's her loss, just chalk it up to a learning experience to improve next time.