Simple answer? Yes!
And, honestly, it looks absolutely no different in polyamory than it does in monogamy. Cheating requires lying to your significant other(s) either by omission (didn’t tell you the whole story, intentionally leaving out important details) or by commission (actually bald-faced lying to their face).
Let me tell you a little story about one couple. I belong to a group for polyamorous people, because let’s face it, being part of a sub-culture – particularly one that either confuses people or pisses them off – sometimes requires a certain amount of social interaction to help people feel less alone. And sometimes, this group has discussion meetings where anyone can bring up something that confuses them, hurts them or they just plainly need more information.
It just so happened that on one of those nights that a couple came in (minimal description to protect confidentiality). She was petite and cute, and he was large and imposing. I won’t lie – I made an assumption before either of them opened their mouths. I assumed the guy was poly, and the gal was confused and maybe a bit hurt. Boy, was I WRONG!
It seems that he had caught her cheating with someone else. When they had the inevitable discussion, she told him that it was “perfectly all right” because she was “poly” and that means she can do what she pleases.
Oh, what a can of worms she opened. And the more questions we old hands answered, the more the guy got the gumption to speak up and ask more pointed questions. He seemed to me, when he spoke, that while he had a definite angry tone in his voice – he was more the kind of ‘large and imposing’ man that tends to be kind, compassionate and loving.
I was, honestly, quite blunt in my own answers to some of those questions. Yes, it was cheating because any relationship being polyamorous is ALWAYS a mutual decision, never one sided. If your poly is one-sided, and is NOT that way by choice (e.g. there are some poly people where only one half of the relationship dates outside people, and both are completely happy with the situation, because they have honest and open discussions about everything) then it isn’t poly in my opinion.
NO, you CANNOT tell your monogamous partner that it is “OK, because I’m poly.” You lied to your partner, either by not saying anything at all or by actively being dishonest.
And personally, if you can’t understand WHY a relationship needs honesty, openness and LOTS of communication (regardless of whether it is poly or monogamous), then do the world a favor and DO NOT DATE ANYONE. Honesty is the ONLY way any relationship works!