Did they do it in his room or something
I don't really know what happens in the context of Chapter 86, but that's just a glimpse of what I see so I'm probably wrong/not, In the end, Cirrus gets comforted by Skylar, here's the context of the panel base on the translation so braise yourself in chapter 87.
"Because I'm worried about you." —Skylar
"This is the first time a person worried about me." —Cirrus
No, it's in his father's room, The father really doesn't want to have sex but the stepmother made him drunk so they did it while the CCTV was on, The stepmother knows that Cirrus was watching in the CCTV so they still do it in the end.
Gosh wtf is wrong with that mother.
I just want to isekai into the world and kill the mother
SPOILER ALERT CHAPTER 86!!!!
Based on the raws that got leaked on some certain social media. Cirrus saw a video where the stepmother recorded her and his father having sex on the CCTV and she showed it in front of him with no shame. That's one of the spoilers I've seen so far, they didn't share the other context of it.
And to satisfy your curiosity about why Cirrus is in that state, he beats up his mother by holding her in a tight grip on her neck. Because the stepmother provoked him, I don't know why but I think it's connected to the CCTV footage of his father and his stepmother having sex.