Where the fuck is the cucking idiot... He said he doesn't like her, and she said hey, how about you see what I have to go through while you are having a more normal life. Her style/playbook is having to do that to get close to the target to kill them.
Sorry if i might've offended you. Though i do still think this does hold a direct relation to cucking, since the guy hiding inside the closet is so closely watching the scene unfurling, the girl is on the bed doing another guy and she emphasizes how she wants him to "watch me properly." It's simply yucky and yucko and the overall gross atmosphere of having a guy watch the girl that liked him having sex with another dude through the slits on a closet, all the while she speaks about "watching her" and saying how she enjoys the fucking, is uncomfortable.
I also disagree with your statement that it's simply "her style/playbook," since if it were her normal protocols or modus operandi, it would be completely unnecessary to have him watch her from inside the closet.
I think this was her form of getting back at him for rejecting her, for "betraying" her feelings for him.
Nevertheless, I don't mean to impose my views, I was merely speaking out of confusion and frustration of having such an unlikeable subject such as cucking in a story i rather enjoy, and apologize for my crass form of speech.
Tl;dr sorry for bad manner, though I still maintain my opinion.