
There's actually some elements of how Hanako would handle the aftermath of cheating on Hisao, that I think are in character (including her suicide attempt)... but her cheating on him in the first place (or being far enough out of her shell to do it) is quite a bit harder to see.
Now, I could also see her blaming herself to this extent for getting raped, especially if she was drugged and didn't remember what happened, just figured some things out after the fact. That would actually make the story somewhat plausible. But, the storyline would have to change, and it'd have to rely on Hanako not sharing her suspicions that she was raped (she's not stupid, she'd figure it out, but she would consider it cheating out of guilt), and Hisao figuring out what she was leaving out.
I actually find Doomish's incomplete story of how Hanako was SOLD INTO SEX SLAVERY after her bad end more believable.