That's voyeurism not cuckoldry.
Cuck is watching someone fuck your partner not watching another couple fuck.
I know i'm nit picking words but so many people on here throw NTR and cuck around at things that aren't anywhere near those.
That would be like me claiming something is one thing while it's absolutely not that thing For example, if I called Amy Schumer a comedian.
But people like this keep throwing cuck around so much it's just a buzzword now, lost all meaning.
Haha there is a game that pokes fun of specifically those poeple, lol loved that game, too bad its abandoned. for now, coming back to the topic, I agree with you on this one, how on earth can it be NTR or cuckoldry when the LI you think you have isn't ever yours in the first place? if anything, let's swap places with the "dad" and have the dad watch the son fuck his wife/son's mother, that will be NTR and cuckoldry, and sadly, we don't get to see that happen often for the correct labelled to be added.
and here is my opinion, let's say even if a mother accepts incest and has an affair with the son, its only on the father will the ntr and cuck titles apply, even if son gets the sloppy seconds by banging his mother next once she slips out after midnight or something having been fucked by her husband, covered head to toe in his jizz lol, in others words, even if the man is alpha, if the woman cheats on him, he becomes NTR'ed and a cuck. that's how the logic should and must apply.
want to be cucked/NTR'ed? have your own LI, legally. xD.