I know...
Did... did she... die?
Oh god, I HOPE not...
Since, if they split, there is always a chance of them getting back together.
But... if she dies, then... sniffsniff ;__;
At least, in a way, we know that they truly loved each other if that were the case!
If you read the afterword it looks more like she was just in puppy love (I like to call it that, when the love is not exactly mature, but still real) and then just split up, well that was my take on it.
The older girl seems to be having a severe case of nostalgia and all we saw were memories.