So the MC won't end up with the original crush/friend? I hope so because that would be awesome!
if this is a 10-part story, then I have a feeling the MCs will go off and date others. once they graduate, they'll run into each other somewhere, remember why they really loved each other, and (cue the romantic violin music) fall madly in love.
on a different note, you have to admit, this is a more drawn out look at the saying "the grass is always greener on the other side of the fence." for example, this chapter is about Nana's regrets after her fight with Youko-chan and how she will deal with them. I wonder if the upcoming chapters will show how Youko fared after their fight? actually, if it does, I guess for completeness sake Takamiya-sensei could look at "the relationship" from all 4 girl's POV especially now that Satomi-san's character has been introduced. however, since mystery GF of Youko-chan has yet to be formally introduced, I personally would have little issue if her POV was really brief. I guess Satomi's POV should be equally short as well... oh well, cue the music, and action!