Is ethical non-monogamy the same as cheating?
No. Cheating is non-consensual non-monogamy — outside connections kept secret from a partner who has not agreed to them. Ethical non-monogamy is the explicit opposite: outside connections that everyone involved knows about and has consented to.
The two structures look similar on the surface — a partnered person also has connections with others outside the partnership — and they are diametrically opposed in the dimension that matters. Cheating relies on the deceived partner not knowing. Ethical non-monogamy depends on the partner knowing. Same external behaviour, opposite ethical content.
What makes ENM ethical is consent that is informed and ongoing. Informed means the partner has the information they need to make a genuine choice — not just an abstract agreement to non-monogamy in principle, but enough specifics about the actual situation to know what they are consenting to. Ongoing means the consent is revisited as circumstances change, not extracted once and then assumed permanent.
The line that distinguishes ENM from cheating is sometimes blurry in practice. A partner may agree to a structure under pressure and not really consent; an arrangement may start ethical and slide into deception as one partner withholds information; what was once disclosed may stop being disclosed. The ethical dimension is not a once-and-for-all status; it is a property a relationship has to keep producing.
Cheating within an ENM structure is also a real thing. A polyamorous person who is open with one partner about another partner but lies to a third — about the second relationship, or about a sexual encounter that violates an agreed protocol — is cheating, even though their overall life-shape is non-monogamous. The category cheating tracks honesty within the agreements, not the count of partners.