The threesome goes down with everyone fully involved. In case you didn’t know, Sasha and Master had already been having regular sex together before this. During the 3some, Master gets emotional and tears up a bit, overwhelmed by the first time 3some experience and by Sasha’s playful teasing—something she loves to do with people she cares about. This is just one panel.
Afterward, Master and Sanada-senpai are hanging out at a fast-food joint. Master has recovered, but Sanada brings up his being teary eyed and jokes about his dick size, trying to tease him about it. But Master claps back, pointing out that Sanada couldn’t handle Sasha either and was also struggling, leaving Sanada with nothing to say. It's all played for fun because this is a romantic comedy manga and Master isn't really a push over.
At the same time, Sanada senpai can’t stop thinking about Master’s great sexual technique and stamina during the 3some—Master managed to climax eight times during the threesome and still had stamina left over for more sex. Sanada’s left wondering how someone younger than him managed to have more "talent" than him, he's distraught over it. To make things worse, Sanada noticed that Sasha was paying more attention to Master, leaving Sanada feeling annoyed. (He basically got used by Sasha for Master, then sees this little newbie boy show off these skills). He wonders how much sexual potential Master has and is worried about it.
So, Sanada gets the short end of the stick (again). Master, meanwhile, just wants to go home and work on his ecchi manga. His post-crying face adds to the humor of the scene, and the two end up feeling like war buddies who barely survived the force of nature that is Sasha (more comedy). That's actually how the chapter depicts them: two adventurers who fought a JRPG monster, Sasha (since the series is not ever explicit).
The story then cuts to Sasha at home happily bragging about Master to her dad in the phone. Her dad, noticing her obvious feelings for Master from how she talks about him, asks if Master is her boyfriend. She's unable to answer at the moment but doesn't deny the idea. He says he’d like to meet Master when he comes to Japan, setting up a future crazy meeting.