Basically, It's their( CUJ & LSY) 3rd time living, before this there was two more lives they lived.
In the 1st life, Cuj was a hunter as he is in the current life and he saved lsy from a dungeon, but as a result lsy was very weak and frailed as he was not an awakened, this lead to many health problems and unfortunately lsy died in that timeline. As a matter of fact, the west sea rift incident didn’t take place in this timeline and cuj was present with lsy in this timeline. They used to live together and shared the same bed and were more than just friends (it wasn’t really made clear by the author if they were physical lovers or just one sided love from lsy). So, after lsy died, cuj didn't find any reason to continue living and tried to reverse the time by a watch gifted by the system with the help of artisan and succeeded.
In the 2nd timeline, cuj again saved lsy and this time lsy was an awakened. But this time the world came to an end (I'm not sure if the west sea rift incident happened this time). So naturally both of them fought till the end and as a result cuj died (it was shown in the manhwa) . This time cuj left his watch to lsy and he also tried to reverse time but the energy balance was off so he got stuck as a variable to balance the end of the world which meant that he didn’t exactly got erased and the 2nd timeline was still there as the story goes on in 3rd timeline. 2nd Lsy was stuck in abyss and as the end will reaproach he will join with lsy in the same body
The end will appear in the current timeline too and lsy will SUFFER greatly. Cuj on the other hand will also suffer and even though he hold such great power he will be completely powerless in this matter. Also not tp mention, lsy was saved by him in timeline too. But as cuj went into the west sea rift and was lost in it, lsy waited for cuj for 8 whole years.
There also factors like -Prometheus, Ga-Young, Matthew and White hole, but this is enough to understand lsy ans cuj's position.
Fuck around as much as ya'll want with these funny scenes, in a month or two ya'll be bawling yours eyes OUT. Heartbroken, hope shattered to pieces, lives devastated and everything, just wait ╥﹏╥