well no, there's Kanashi, but she's blonde and there's only one blonde girl dancer in the PV xD
rest has black hair, so it's three of them left
OK, back on topic.
Why did Ayu look so in-Lovey?
Well... She's been on tour. Working. When you're working, after the job is done (or halfway done), you're all tired and feel lovey-dovey, don't you? So she probably did. She wanted to get close with somebody and Shu-Ya probably was the only one brave enough to start acting like that towards Ayu.
xD