I originally interpreted that as just a result of high emotions, due to losing her best friend
Nah, it throws them back to school uniforms aka the beginning of the story. The end happens 1y+ after they finished high school.
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.
I just see glasses as a good friend and confidant for blonde, who was always in on it. She comments when the brown hair "finally agreed to it" and was there to lend a shoulder when it finally went bad. I don't think there is any point in looking too deeply into it.
The angst here felt forced. Forced misunderstanding is something I've found to not only be very common in Korean manhwas
I don't really see how the angst is forced. It's not spelled out, but it's basically the same as everywhere else: they both want to be with the other, but they are scared that if it doesn't go well, they won't be able to keep their current relationship, etc. It's not really a misunderstanding, it's just a lack of communication and guts to take the risk.
After thinking about it for a bit, considering minimalistic presentation, I don't think it should be deconstructed and scrutinized too literary. Not sure if that was the author's intention, but for me, it's more like a fairy tale with a moral. Sure, they both could have done more in various situations and salvage it too, some of it didn't make too much sense, but that's not the point.
I also really like that brown hair is not portrayed as a cookie-cutter "perfect best friend" who will stay close to their crush even when she's hurting. There will be plenty of people in life that will not act selflessly and graciously, because we are all flawed, and sometimes we might just decide to run away from pain instead of baring it.
So shot your shots before it's too late, and don't leave important matters for the last moment, because you never know when it might, out of nowhere, go wrong.