What does she mean by it's okay? I am afraid of being destroyed day by day.

This is JJ Lin's, she said. The lyrics mean that what she once said is not important, but I'm afraid it will be destroyed by powerful forces one day.

There is nothing wrong with two people falling in love, but they are separated only because of each other's lovesickness, which is a kind of torture for both of them, but she thinks that the promise can bear everything, so it doesn't matter what she says, but then she thinks that it doesn't matter what she says, that is, the promise will be diluted by time until it becomes a joke, and she can ask questions if she doesn't understand.