Pammy:
It's important for the drama's english title "lost you forever" tho?
The title of the novel can be translated as "Eternally Yearning For You". That seems to refer to ZX's yearning for XY.
It has three volumes, and the first volume (chapter 1 - 17) is titled "Lost You Forever". Which I don't really get tbh. It seems to only make sense if it's referring to ZX and XY losing each other for what seems like might be forever, but ends up only being a little over 300 years. Perhaps with the added factor that ZX's choice to pursue the power to protect XY at all costs ultimately means that he must forego love, and thus he is doomed to lose XY forever from that point on in a sense.
The second volume is titled "Telling of a Sorrowful Love". This seems to be referring to XY's love for Jing, but could also refer to the doomed feelings between XY and XL, or ZX's unrequited feelings for XY.
The third volume is titled "Missing You Without End". XY misses TSJ for seven years, but that has an end. XY leaves ZX behind after XL dies. She could be missing either or both of them without end, and ZX will likely miss her without end.