in my opinion, I think it's about a guy who's miserable because he likes/loves a girl that just keeps falling through his fingers, and her dancing represents her playing hard to get. As she finally becomes real, and perhaps in a way says to him, 'I'm ready to be with you now', it's apparent he's grown tired of the games, and walks away.
I could be completely off the mark, but that's just how I interpret it when I see it.
Most Helpful Girl
I think there are many ways to interpret this.
My initial thoughts were that maybe the woman was someone who had died, and the memory of her kept lingering in his head. But as time goes on, the guy is letting go, growing tired of remembering her, until he lets go of her completely.
The woman playing hard to get could also be an interpretation.
Another interpretation could be that he keeps fantasizing about a girl, but once he musters up the courage to actually get to know her, the image he had of her was not enough and the real her was a disappointment. So he then leaves because the expectations weren't met, hurting her in the process because she was really into him.
Most Helpful Guy
I am close to your interpretation - I was definitely feeling a "Lost Love" or maybe she died in the first 95% of the animation but as you say at the end she got real and he walked away. Lots of ways to go but I will go she is remembering being in love and a separation, I think she is one in love and for some reason it breaks, he rejected her or died (I am getting a strong vibe of dying whether a person or love I am not sure). That is my main theory.
My second theory is she betrayed or cheated him and realised she was wrong. She came back looking for forgiveness and he wouldn't give it.