There's a few artists who do really good NTR stuff, even if it isn't their primary thing. CheekyNTRbuns, AT, Combos & Doodles.
There's two good NTR doujins I remember really liking, too. There's one by an artist called Denchi, the name of which I don't remember, but it's a six-part series about this girl who locks her masochist boyfriend in chastity and openly cheats on him a bunch. Shindo L also did a really good NTR manga with a really strong writing focus (maybe this is a hot take but Metamorphosis/Emergence wouldn't be so infamous if Shindo L wasn't such a compelling writer).