Why is this situation so confusing?

So I feel this girl likes me so I stick around, but then she does something really b*tchy then I move on. She then acts nice and really flirty and basically won't let me move on. She gets jealous of other girls I give attention to, she flirts a lot with me, and she always teases me. Though the weird thing is when I text her, some days she answers really nicely and continues to write long message back to me, then other days she doesn't even reply. So it's like she gives some, then takes it all away. A while ago we went to the movies and dinner and we really seemed to be having fun together, but I didn't know it was a date so I didn't ask her again. Then a few months went by and she brought up to our friends that we went out on a date, so panicking I ask her out again later that day and she says she'd think about it, only to say no. So far, I've asked her 3 times and she's said no. I asked her if there was some reason why she says no and she said maybe. I just don't understand why she gets jealous and flirts with me and never lets me actually move on. What do you think?