"I think the term “cheating” inherently means that the person not involved isn’t fine with it. "

Is precisely correct.

Edit: in clarification. If your stated, mutually agreed upon, boundaries aren’t being broken then you aren’t being cheated on. If you’re ok with your partner fucking other people, but told them you aren’t for some reason, then I guess them fucking someone else would technically be cheating. But you should really learn how to accurately describe your boundaries with your partner.