I'm not sure if this is true but this is what I found on another website that someone summarized. "Ok so basically after they defeat the demon lord they have a celebration and during that time, the MC friend finds out that the MC is fucking “his” female and so they fight. The MC ends up winning and killing his friend. Then theres a scene where the MC is pouring out his real emotion about how he actually wants to have a straight and “main-character-like” life, just like his friend that he truly “respects.” And so he wishes for everything to go back to the beginning (think of it like FFF trashhero) however, in his new life he doesn’t become friends with that guy and they each go their separate ways or something along those lines. Well anyway, that concludes Volume 1 of the LN."