Her sense of security > You being kinda horny
Cucking and hotwifing is fun, but her saying "I would feel bad if someone other than you put their cock in me" should be the end of the discussion.
Negging/guilting her into some weird situation that even the other guy feels bad about is only going to make everything awkward.
Like if you bring it up and she doesn't go "I was waiting for you to ask!" then it's only going to end in tragedy when she feels like she's sacrificing her morals/body/safety because you're a coomer who can't stop wanking it.