Oh, hi, adorable anon! Sorry for replying only now ^^;
Btw, oooooh, yes!! A kink question!!!
Ntr, huh?
Ok, I'll be honest. I kinda have a netorare fetish. Or better, it's more a cuckqueaning fetish. I get very horny at the idea of my bf having sex with other girls. I don't know if I would enjoy it IRL, but I LOVE when he pretends to have sex with other girls, like his waifu, and him having fun with them in front of me or without me... I don't know, I feel soooo happy!! I see him being very happy and I feel very happy too!! I feel a huge joy when he talk about how attractive they are, how he loves them... I don't know, it makes me incredibly wet and horny XDD
Also I admit I like the idea of having fun alone with his waifus or girls, even if I'm not attracted to them, because I know it would make my bf horny... I repeat, I don't know if I or we could handle it with actual people, but as a fantasy between us is soooo much fun!!

So... I think ntr kinks are totally fine in relationships! If it involves real people, it's always better talking with the partner previously of course ^^
Even if they like being cheated on, I think it's still important to warn the partner, as a sign of trust and communication ^^

So, yeah, totally fine with them! Have fun!! ^^