Hen Zemi: Komugi harbors this particular fetish,and actively tries to invoke it with his girlfriend.
If a shoujo or josei manga has a Bastard Boyfriend as a male lead, it'll have at least a NTR variation in the plot. I.e., the infamousSensual Phrase scene in which Sakuya snaps on Aine, drags her home by force and barely stops himself from raping her comes from a misunderstanding in which Aine was unwillingly given a hickey by a Hopeless Suitor and Sakuya thought otherwise. And Haou Airen has Hakuron raping his girlfriend Kurumi in front of her newfound friend Kaafai when she leaves him, to force them see that Kurumi is with him and only him, as well as Kurumi having Sex for Solace with Hakuron's Dragon Fuuron despite being still with Hakuron, and Reilan trying to get Kurumi gang raped in front of Hakuron specifically to taint her in the eyes of everyone. (Two of the three HA examples, however, backfire HORRIBLY) .
Nozoki Ana: A very huge, hurtful example that many readers were predicting for ages. Not only was Yuri Kotobuki, the girl in this situation, cheating on weekends, but she decided she'd rather have sex with her rich boyfriend instead of spend Saturday with her other boyfriend, the lead male Kido. On Kido's own birthday.
Alluded to in Air Gear, with Hako referring to Ringo as "NTR # 1" and accusing her of cockblocking either her or Kururu, as they both squabble to become Ikki's link turner. Ikki chooses Ringo anyway.
Similarly, the Fate Zero fans refer to Kayneth, his fiancée Sola-Ui and Diarmuid!Lancer (whom Sola-Ui falls for) as "Team NTR". This isn't exactly an example: Diarmuid had no romantic interest in Sola and she probably never cared for Kayneth to begin with, as their engagement was an arranged one and she was not happy with it. Kayneth certainly felt NTR'ed though.
A minor meme in Bleach refers to Tsukishima's powers to brainwash and manipulate people into loving and caring for him as " Tsukishimawill get you NTR'd".
A large portion of H-Doujin of Ah! My Goddess are NTR. So much that they make multi-volumes from differant artists. And with the revealed that Heaven surpress Keichi's urges towards Belldandy and her knowing all about it, all of those doujinshi take an interesting twist.
In Berserk, the first thing the newly transformed Griffith-turned-Femto does as a Godhand is to rape Caska right in front of Guts, who is Forced To Watch. Guts can't do anything but cry at the horrific sight as an Apostle pins him down, gouging out his eye in the process. Made even worse with Caska's last words before losing her sanity: "Don't watch..."
In PITCH, Light has sex with L and, after tying him up and gagging him, forces Aiber to watch. It's different in that L and Light are already together, and Light is trying to make Aiber realize that L is not available.
Defied in Reconciliation, a Katawa Shoujo fanfic in which Lilly and Hisao get together after Hanako's bad ending and Hanako, despite having isolated herself from the two out of guilt, harbors feelings for Hisao. Word Of God states early on that the fic is not intended to be NTR, and in the third chapter, Lilly calls Hanako to tell her about Hisao's death.
Indecent Proposal, in which a millionaire (Robert Redford) offers a young and broke couple (Woody Harrelson and Demi Moore) a million dollars in exchange for a single night with the very attractive wife.
In Paul Di Filippo's short story And the Dish Ran Away With the Spoon, the heroine is stolen by an intelligent assembly of household objects, including a vacuum cleaner, a food processor, and a blanket. That hurts.
The Irish ballad Seven Drunken Nights is sung from the perspective of a man whose wife is cheating on him.
Jairo, "Para verte feliz" ("To see you happy"). It's sung from the POV of a guy who knows his beautiful girlfriend's old flame is coming to town and chooses to rather have them almost tongue-kissing in front of him rather than confronting and then losing her, since he's that much of a Love Martyr towards her.
Ancient Bloodlines speaks of a vampiric Babylonian priestess' lesbian lover being taken from her forcibly by the En emperor. Turns out the lover eventually fell for her abductor in typical NTR fashion. Unlike other netorare stories, the priestess got her revenge on them by creating the Iltani and edimmu.
Tends to happen quite often in The Sims, especially if you're not careful with relationship management and/or don't have a No Jealousy hack installed and decide to have a threesome or Love Dodecahedron.
In Grand Theft Auto IV, Vlad reveals after a mission that he has been sleeping with Mallory, the girlfriend of Niko's cousin Roman. When Roman finds out, he is understandably distraught, leading Niko to chase down and kill Vlad. Weirdly, this actually results in something of a happy ending, as Roman lies to Mallory and says he did it and she is impressed and touched and even a little turned on, and their relationship improves, culminating in a wedding. Of course, your choice for the penultimate mission can lead to Roman getting killed, but...