Ah, so the ML is the black king, the FL is the scarlet witch, the other girl is the white sage and McStabber is the "Hero". It's definitely not his first time of killing those three, and he's most likely went through so many loops that he doesn't even remember why he's doing it anymore; just an automatic process.
How will the cycle end? That's the big question. The Hero probably had legitimate reasons when he killed them the first time, but are the reasons still valid? Will they convince the Hero to stop or will the Hero die without killing them? Heck, maybe they even become a team and the Hero rejects his fate or something.