Nemureru Hana
Complete | Ebihara Yuri | 2006 released
To me a happy ending would have been Masumi ending up alone (or at least not with Ryosuke). She was a bitch (I think everyone got that one clear in the comments). Just wish that in the genre info alongside you it said psychological. Surely wasn't in the mood for it.
Sono Te Kara Tsutawaru