I was wondering why this got an Erotica rating when it was just Suggestive last I read it.
Damn, this escalated massively once they crossed that final line. Then as expected after losing themselves to pleasure, it turned into a hentai-esque literal montage of public sex, self-harm and drugs. Not kisses, not love, not even sex ends the loop. No wonder they truly went crazy. Although I'm not sure if Mashiro disappearing near the end was just her breaking up with him, or if she actually escaped the loop before he does. She did get trapped long before he did after all.
Hell, it seems he started having other partners too... like class prez Yoshino (glasses girl) and Momo (black-haired karaoke girl) so I guess even love with Mashiro died out in the madness of the endless loop (assuming she didn't escape before he did). Hell, it seems even his own sister was one of the black-haired girls in the montage. What a way to underscore just how crazy his life went.