This is one of those things why communication is important.
"I want you to watch".
Haters: fucking scum, pervert, wanting to live his porn fantasies.
Him: If we did this behind your back, I'd feel like I'm betraying you. Plus, you'd be anxious, right?
Not that the girl has to enjoy watching it, but she can choose to stay. And if she leaves, well, he WAS thinking of her first.
@gryffinp Tbf, I wouldn't put much trust into this manga's terminology, if any. The girls' cups are completely wrong.
They keep saying "two-timing" when it's NOT two-timing.
And now NTR...well...I guess kinda sorta? But we could still debate it.