I guess see how she interacts with other "guy friends". Some girls are just REALLY flirty because they LOVE the attention. I knew w girl who strung a guy along who was head over heels in love with her, but she didn't return the idea. But he follwoed her beck and call like a puppy, whatever she wanted he bought, whereever she wanted to go he took her. He was determined to change her mind and get her to like him (she ended up with a boyfriend of her own later).
It's awful that anyone would do that, but those are the people who are self-serving and you don't want to be anyone's footstool, right?
My thought is, she strung you along and you missed a few red flags in your eagerness to progress things
