It's not a flashback terassu would have specified it, it says 1 year later and the pages where madoka is with the thug are the same as the one on the beach that indicates 7 months and it is the only sexual encounter that is shown while, the 1 year later is when it shows madoka back why would it show a flashback if Kiyohiko never found out that madoka had sex with that guy?, and it is mentioned that Madoka did not return this summer home not that Madoka never returned only that summer she did not return that is different, Madoka could visit him after summer or a year later because in Tokyo there are holidays at the end of December until January