It very much IS ntr, but f95 is welcome to say it's not.
ntr- is a more sublime version of cuckolding/cuckoldryIf her husband would know she is cheating and can't do anything about it, then yes, that is NTR. But her husband is clueless, so that's just cheating.
female (or male) is f*ed by other, it’s gives the watcher two feelings, sexual satisfaction and torment.
Its something like sado-maso cuckolding
or...
where a female (or male) is mentaly degraded or raped against her will, but after a while she begins to feel satisfaction about it, which she manifests to his legal partner.