If that's the case then I can see why there's so much arguing about NTR. That's a pretty meaningless distinction to most people I would think.
Well, if someone asks about ntr, I answer about NTR and not about something he didn's ask for.
The definition of the term is given, you can ignore it if you want. But then you are also free to say that shoe laces count as bondage.
I admit, 'catching' was the wrong term, 'seeing' was the right one.
NTR means that the protagonist sees his loved one being taken by someone else.
There are 3 points that define it
1. It must be viaual. The protagonist must see, but many even count the display on screen without the protagonist present as ntr, even if that's not right. ntr has nothing to do with screens, it's a storytelling aspect.
2. The protagonist does not consent, so sharing and swinging don't count
3. The 'lost' person is someone the protagonist has a romantic relationship with. Unless they start such a relationship, the protagonists mom does not count.
But even if we ignore the whole debate about what's ntr and what's not ... from a gameplay perspective, these scenes can be avoided. QED.