People have different joys and sorrows.
The happier Gu was, the more miserable Old Chen felt.
There's nothing more painful in this world than watching the guy you like show affection to another girl, especially when you can't oppose it or even show your feelings.
What's even more painful is that—in front of a girl like Jiuyue, you can't even find any reasons to console yourself.
I'm prettier than her, I'm more considerate than her, I can help Su Huai better... Bullshit, nonsense, absurd.
The usual self-consolation that ordinary girls rely on doesn't work at all when facing Gu Jiuyue.
Chen Nuanhan couldn't find any aspect where she truly excelled over her, and the more she compared, the more desperate she became.
And the reason why she still maintained her last bit of pride was partly because of her natural stubbornness, and partly because of Gu Jiuyue's health.