@mommunism
She never experienced love of the romantic kind.
By telling her he loved her when she had resolved herself for death and convinced herself she’d lived a fulfilling high school life by avoiding a life-saving surgery that could have made her miss all that, but live longer in contrast...?
It gave her more to think about. Maybe she was in love too, and was in denial about having been satisfied. She might have imagined a future where they could have lived together happily, had kids, etc. That “happiness” she never got to taste could have given her despair, or regret. It’s not hard to see.
This girl is clearly a wild blooming flower, weak and fragile, and dying quickly, having convinced herself she’d live a fulfilled life that way rather than being in a “greenhouse” or hospital, kept alive, but not really alive... but there was a future in that path she could have taken and had far more time allotted to her, would the surgery have been successful.