Regardless of anything else, given the context that you JUST got from hearing a personal, tragic story, what the hell kind of a response is "Hey, at least there's the other!" from the current supposed love interest.
Now this is the first and only time we've seen his girlfriend aside from a few mentions prior and apparently they don't know about Kaoru, so I'm going to chalk this one up as the author writing in a character just for us to hate them right before they never show up again.