Take this formula: girl meets boy in bar, thinks nothing of it. Ends up casually seeing this boy for several weeks. Refuses to decide if she think it's anything more than casual, even though it seems like he'd like it to be more than casual. Grows unwittingly (or wittingly but without admission) more attached while maintaining to herself the relationship's casual nature. Continues "casually" seeing this boy for several more weeks, verging into the multiple months territory. Suddenly becomes wittingly more attached/admittedly attached at the precise moment when the boy starts to ignore her. Decides to, as best as she (in a somewhat emotionally stunted about relationships way) can, put it out there that she'd like to make this less casual. Learn he did make it less casual. With someone else.
The argument could be put forth that, since while it seemed he was looking for something casual she was looking for something less casual, she sort of had it coming. On the other hand, the argument could be put forth that she misread the signs and had no real reason to be surprised when this abruptly blew up in her face. The argument could be put forth that at least she tried, and isn't that something? And all these arguments have their merit.
The thing about these arguments is they don't account for the part where the girl can't help but just not get it. What changed, and when. They don't account for the part where the girl always assumed that if and when this DID blow up in her face, it would be because he was bored or busy or not looking for anything serious. They don't account for the part where he was looking for something - just not with her. They don't account for the part where she can't stop asking why not her. They don't account for the part where it's about him, but it's more about the deflation of that scary but great feeling where she thought this could really be something.
But these are all feelings contingent upon a real relationship, she'll think. These are all feelings she doesn't necessarily deserve to have, so she'll stuff them down as best she can when talking to friends and pretending that she knows she's making it a bigger deal than it really is. These are all feelings she shouldn't have when being blown off by someone who very likely didn't care very much in the first place, or very likely wouldn't have mattered much in the long run.
The trouble is, the girl is me. The story is, the girl is me. And the trouble is it's not a story at all. So for the next few days, I won't send the passive aggressive text and I will continue pretending it's not a big deal. But it turns out? This still kind of blows.