Yeah i know right? I searched up the novel when I couldn't wait anymore to find out what happened and I saw that there was a separate second part after the first one. It starts right where this chapter left off and actually concludes the story
I read it a long time ago so I can put down what I remember but I don't know if it's all getting adapted.
So the ML regressed after mc sacrificed himself and basically just does everything over again but this time he watches our current mc's body and waits until the day that he remembers him saying he switched bodies. He gives him the slave ring again but this time ML is the slave and MC is the Master (it might not be the same rings or it's a lovers ring now or something but I can't really recall)
ML takes MC back to his guild where bundles is waiting for him. MC can't remember bundles so he takes the orb and hits MC with it. The orb is that thing they got from the nightmare monster they fought before. It acted as a save file for his memories from the last regression and MC remembers that he sacrificed himself for everyone.
They then send the orb to the scientist who figures out a way to use the orb and the memories within to have everyone remember the previous regression but it only works with the memories they share with MC because they only have MCs save file.

So the novel does technically end here but there is another novel. I dont know why it's separate, but mc gets his memory back from before the ml regressed after his death.