^ Althought that's not personally how I see the PV...I'll try to explain.
The world Ayumi is living in in GREEN is basically a fantasy world. She can walk around the streets without being hassled, she can be with the person she loves. And the same would apply to the males.
But also at the end we see Ayumi sad, because we see that she isn't living in a perfect world. Her leaving at the end into an empty street to me symbolises her loneliness.
Also it could be extended to homosexuality...for the majority of the PV she's living in the open, she's being with the person of the same sex she loves, surrounded by people who're "like her" but then when it's time for her to leave once again she's all alone. Which is how many gay people feel.
That's just my intepretation. I've also heard rumours that GREEN's PV is based on a Chinese film called Lust, Caution. But you'd have to decide for yourself what you see.