I can’t understand girls?

There is one girl in my gym. She always look at me, one day I saw her staring hard lol. I talk to her, she laugh, it looks pretty good, them nothing happened, I try to talk again, she respond, smiling, looks happy but don’t engage and I let it go. I compliment her, but it looks like a one side thing ( she does reply) I gave her space and she start to avoid me. I did nothing, even avoid her too. Till one day I say” ok f it, I like the girl if she reject that’s it”. I go talk to her and I never saw anyone look so happy to talk to me. Really it made my year seeing how happy she was. Maybe I like her smile too much at this point. Any way, next day she says hello for the first time, and after that everything goes to zero again, even I trying to talk and etc. she just goes from cold to hot to cold. One thing o realize is that she does start a approach almost everyday, but stop herself. The problem is when I talk to her after seeing it she don’t engage or say anything that I don’t ask.
I can’t understand girls?
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