I didn't see anyone saying they wanna see them bang other people, but it would be normal and they wouldn't mind seeing them ending up happy with another character. Also it would only be cucking if you were in a relationship with the girl. If she is dating the person who she is having sex with, that isn't cucking.
From all the main girls, Side girls, I haven't seen any sex scene of them with another guy. Even Elena and Heather who are dating Tommy and Johnboy.
"Some people plays all the routes and it will feel weird to see my main girl with another dude." Meaning: I wanna fuck other girls, but while I am at it, I don't wanna know that the other girl who I call main, but left her to fuck this other girl, is together with another guy and eventually fucking him lol.
Totally male behavior.