The time we spent together was too little, only a few months
But the love I have for you and the hatred I have now are five hundred years old. This five hundred years should generally refer to a long time.
When it was time to say goodbye, Fang felt it was too late and shed tears in Guanghan Palace. This should refer to a sense of regret
The meaning of the next four sentences should be. If this affection is not (reciprocated), you should lock this feeling there, put it in your heart, and forget it. Let it turn into smoke and disperse.