Nice, except for one thing:

Every part of me is screaming that this is wrong; that I shouldn't
betray my best friend even for one moment of happiness. But his
warmth, combined with the scent that is uniquely his overpowers
all my urges to bolt.

Keep in mind that in the movie, Hikaru believes that things aren't going so
well between Kyosuke and Madoka (a mistaken impression Kyosuke never
corrects).  She thinks he's more-or-less "available", and wants to be his
girlfriend again.  She *wasn't* interested in a one night stand at all.

Indeed, when he calls out "Ayukawa", she immediately realizes that he's
still in love with Madoka and immediately backs off.  But she's *not* giving
up; she tells Madoka that in so many words later at the pool.

This is clearer in the novel (on which the movie is based); MI wanted to, in
effect, recreate the triangle.  I'm unconvinced that he successfully did so,
but that was his intention.

Otherwise, I really liked this.  Kinder bittersweet.  I prefer Madoka, but
I've always like Hikaru, too.  The manga version was pretty much betrayed by
Kyosuke and Madoka, and didn't really deserve all the pain she got right at
the end, so it was nice to see her get a small measure of happiness from
Kyosuke, fleeting as it may have been.

-Richard