tbh i dont find it all that shallow. i knew a lot of girls who wouldve gotten mad cuz their bf thought their friend was hot, probs would have fought with that friend but they both mutually decided that that wasnt worth it and dumped guys that looked at their friend like that. i think it was just to show how close the girls were
Keep in mind that this is my opinion and that I know it's a manga ;)
It was more about how they break up with them for no particular reason, like "Hey, I just got bored, let's call it quits". If they didn't like what they heard, first don't ask and second, you tell him, you et mad and the sex ends there. Cause one guy tells how he wants them to be together forever and the other tells the girl how great it is to see her after a tiring day. They say veautiful things, they have sex, nothing seems wrong in the couple. And the guys were just answering to their question of "What do you think of my friend?". Being a girl, I know they wanted to hear nice things and the guys knew as well. Cause if a guy tells bad things about your best friend, he must be ready for pain...
*beautiful
The way they leave their bfs... I just hate it, it's that fickle, shallow depiction of girls what I the hate most in shoujo mangas.