Have you seen Akane Maniax, Yuki?

Haruka suffered pretty badly as far as I'm concerned, as did Akane. Haruka lost the one she loved, came to the realization that her accident, which wasn't even her fault, ruined 3 lives (Takayuki's, Mitsuki's, and to a less extent, Akane's) and had to deal with the knowledge of that for another 2-4 years. We see her in the KgNE epilogue happy (if a little sad still) but certainly functional. The Akane Maniax OVA takes place in between and shows a rather different picture. She sits in the dark, clutching the picture book, alone.

If anyone is to blame for all the tragedy of the series, it is of course, Mitsuki. Moreover, she knows it, and paid a huge price for it.

Mitsuki delayed Takayuki in order to have him give her a "birthday present." A ring is far more symbolic than a simple birthday present to a friend, especially considering what finger she puts it on. Furthermore, she hesitates just a little when she tells him it is her birthday, so we can't even be sure she's truthful about that.

Mitsuki had to deal with all that guilt. She quit swimming (and as a result, angering Akane further) and never went to college, where a she would have gotten a free ride on a sports scholarship. She became a simple OL, and had to deal with everything that she knows she was the cause of. That's part of the reason she goes to comfort Takayuki. Then, even though she knows she liked him for a long time, Mitsuki still feels awful for "stealing" her best friend's boyfriend. All this guilt is magnified when Haruka wakes up, and Mitsuki eventually breaks down.