@Tamerlane
I totally agree; the personalities involved are volatile, passionate, and (to a degree) selfish; yet they suddenly lose ALL of that... except Nino, who is then painted as the classic "woman scorned."
Which she is, but... it seems as though Futaro just doesn't have the emotional range of a turnip, and is simply interested in the easy option. The person who didn't really cause him any trouble, or display very much emotion towards him.
Which would piss me off unbelievably, and I wouldn't want my sister to date a guy like that... of course, I wouldn't want to date a guy like that either, so maybe this theory is all just in my head...