There's something I don't quite get.
She says the white tulip is the other girl's favorite flower, right? Text literally says "her favorite white tulips" are embroidered on the handkerchief.
Okay then questions:
First, why is her favorite flower one that means breaking up????
Second, why does she assumes that the hanky with the white tulip means her gf doesn't love her anymore, instead of assuming her gf wants to make her happy by giving her something with her fav flower on it? Maybe I'm missing some point but it doesn't seem to make sense.
I think it's because she's reading too much of her partner's action since Her gf who are the type that only watch happy ending, suddenly ask her to watch sad ending movies. She even said that she's too focused wondering why her gf ask her to watch that movie instead of enjoying them. Still left unanswered, and then her gf gave her that white tulip handjevrdhd out of the blue, so she think and try to connect those two out of the blue occasion and end up with that conclusion