Really, the only reason we might not come to that conclusion
Since blonde is blushing on the very last image, in contrast to the image presented by brown hair narration (holding hands, where only she blushes), I think it's implied that it was mutual.
I originally interpreted that as just a result of high emotions, due to losing her best friend, but I could see it your way too. I didn't notice at first, but the person she's crying too seems to be wearing pajamas (or at least that's what I normally associate that sort of blue and white pinstripe with). Not sure what to make of that choice.
You could just as easily say it was the blonde's fault
I don't think there is any point in blaming anyone. Blonde was asking about boys, brown hair was replaying about boys. They were faking each other out. The issue is that neither had the guts to take the first step, and that's the cautionary tale of the story. And by the time blonde made a decision, it was too late - brown hair decided to move on and cut ties to not get hurt more. Another cautionary tale I suppose - hail mary at the last minute won't always work, for one reason or another.
Agreed. I was trying to push back against the idea that that Brown Hair was being dense or that the drama was forced, rather than this being a reasonable result from two inexperienced teens trying to feel each other out and missing their opportunity.
I don't understand a lot of stuff. I don't get blonde girl, was she supposed to be in love with the other? The talk about boys, it was a smokescreen? Was she waiting to last page of the diary to write her confession?
I don't understand either who's that other woman with glasses, in page 4, consoling blonde girl who cries: a new character? a future lover? Is she listening to the same story from the blonde's pov?
Too little info, too much guessing to do.
The answer to the first question is somewhat ambiguous. It's implied that might have been the case, but it could just as easily have been entirely platonic on her end. Similarly, the talk about the boys could have been legitimate interest on the blonde's part, an attempt to feel out the brown haired girl, or an attempt to stay in the closet until she was ready.
We don't know what was on the last page of the diary, which is sort-of the point of this story. The Brown haired girl refused to read it, out of fear of getting hurt, but the question of "What if" has haunted her ever since, to the point where she's telling her girlfriend about it years later.
The other girl on page 4 seems to be Glasses Friend from page 2, though we don't know anything else about what was going on and even that much is a guess. Again, all of these unanswered questions are part of what this story is trying to show us. The main character is struggling with them too and envisioning different ways it could have gone with no real answer. Showing us more, as readers, would lessen the impact of that message.