Don't question it, don't think anything in this story has any deeper meaning, it's really just a fan-service riddled mess 🥲
Girl thinks he leaves, because some hickey would make him feel so extremely guilty, but she wants him to stay and get closer, yet every chapter he hears moaning and is seeing things implying she's fucking someone 😐
Dude gets upset, because he thinks the hickey is from some possessive boyfriend, but is fine hearing her fuck around, while living with her and plays 70% of all chapters as monologue in his head, instead of actually opening his mouth and having the story progress 🫡
Gonna assume that's going to drag on for a long time and, then he probably finds out she has a sexfriend or something along the lines, which he is probably perfectly fine with 😶