I can't believe I'm answering this lol! XD
To be completely honest, I feel that some important aspects of this manga are flying over a lot of people's heads, who are too busy lamenting the lack of yuri or hating on the guy. I feel that the main problem is that we were expecting a romance, when this manga isn't even tagged as such. I don't think this story's central theme is the girls' love for each other at all. This manga is about the protagonist's feelings and growth as a character.
Honestly, I want a good story. My favorite mangas of all time are all extremely light or vague on the romance department. I'm not expecting a straight up hardcore yuri flowery love fest (though I like those a lot too). What I want is a good story. However, the yuri genre tends to have better romances from what I have experienced thus far.
So then we have the little arc of her ignoring her friend as punishment for liking the guy she hated. Now, regardless of whether you feel that her friend is a terrible person or not for liking the guy who calls Youko "Imoko" doesn't come into the equation here. What that arc was about was that Youko was playing it tough and giving her the cold shoulder on purpose out of spite, and she KNEW that. It's not "hmph, bitch deserved that." It's "crap, I'm hurting the girl I'm supposed to love, and yet I can't seem to stop because I'm too angry." That's what Youko is feeling during that arc, and I think it's amazing because it's such a human thing to do. I don't think I'm the only one who has ended up saying/doing hurtful things to the people who care about me because of my petty anger/frustration/jealousy. She's such a human character, and I love how in this manga it's not like she has a sudden realization that she's hurting her friend and suddenly gets over it and goes into full "I want my beloved to be happy" mode, but instead has to keep struggling with her negative feelings.
Youko's friend completely ignored the fact she was insulted, humiliated, and offended by his actions. Most people I know of who had friends that did this have their friendship seriously threatened or it's broken up and almost never repaired. I saw no decent character growth here when there could have been some real solid growth for a character to actually move on from a friend (which I rarely see happen in romances).
Now, even though I don't really like Keita as a person, I think that he, as a character, is a perfect foil to Youko. He is shown to be a dumbfuck who doesn't realize how what he says affects other people. He's annoying, rude, and gets in Youko's way. But he doesn't have bad intentions at all, and is shown to care enough about his Kouhai to go out of his way to apologize for something he didn't see as bad, just to get them to reconcile. I'm not saying he's a good person, nor am I saying he's a bad person either. He's a human, too, just like Youko, with good and bad points. I believe that Youko learning to deal with him as a person and accepting his good points as well as his shortcomings is a big part of her character development. She was demonizing him from the beginning, while later in the story she's shown to see him a bit more as his own person rather than just an asshole. She still hates him, but she also starts to understand him a bit, and if you don't think that shows how great her character development is, then I don't think you and I have the same definition of character development.
Just to reconcile for the sake of reconciling is a pretty big douchy move on his part since he didn't take the time to really understand Youko's position. Then he continues calling her Imoko and turns it into her identity after she was clearly offended and hurt by it. Lastly, her friend has been spectacularly unsupportive of Youko this entire time. Youko growing as a character would have been to dump her friend after the initial bout about Keita and then no giving in with him when they first tried to reconcile. She's also coming across as a bit of a lone wolf since it seems everyone is sticking up for Keita and not really trying to tell him off when he's hurting Youko or giving her more support and advice. And her character development seems to be the only one trying to make any headway, like pushing against a crowd. That is why this is very frustrating for me. I felt like it had a few chances to really see the whole cast have some parallel development but instead we do and don't see it with Youko. Also, my huge disliking of Keita stems from the fact I knew a guy in my high school who was like that. A lot of people became very annoyed with him because he never took anything seriously and was always goofing around. When he started going to far or just getting on people's nerves we'd tell him off, and this went for a whole range of different personalities. Thus my dislike of Keita comes from that and also just how the story has been progressing.
Also, this has far more yuri content than Stretch which has very very subtle hints that only people wearing incredibly thick yuri goggles can claim to be seen. But for me, I usually want a good story first, and a romance second. The het storyline isn't an issue as a plot device but it becomes an issue with how it's been written (especially in this instance). Like you, I think Youko as a character has shown SOME character development, but it's hard to measure when no one else seems to be growing alongside her. She showed me a lot of potential initially but I felt like she missed some very big chances from growth which made me wonder if she was "out of character" for those scenes just to prolong the drama. (I.E. the author created these characters but when one's personality would take them in an entirely new direction, the author didn't want that to happen so they did this and that instead. Basically, I though Youko had more back bone but when it came time for the show down she didn't stand her ground the way I thought she was being portrayed. That made wonder if she was written out of character.)
