I am thinking that perhaps in a situation whereby someone cheats in poly they are possibly getting lax. I might be wrong here, but I for one get tired sometimes of the constant communicating and honesty, if someone thinks that for sure they know it will be okay to just be with someone one time because their partner won't mind then there is some complacency going on in my book and that might mean reining in a little to reconnect and establish some new boundaries around assumptions such as that. No one ever knows for sure, but when things are ticking along and we start thinking that nothing can touch us, it can happen that some un-discussed fucking can come about
that doesn't necessarily mean throwing in the the towel on Poly, but reconnecting on boundaries. Really, coming together to get on the same wave length sometimes can be a good idea.
Is it okay to just go with assumptions that we think our partner will be okay if we sleep with someone without them knowing? Well sometimes it is and it is okay. A boundary is established without really discussing it... but sometimes there is an eye opener for people that means that there is actually some boundaries to discuss and that it isn't necessarily okay to do whatever, whenever. It really depends on the couple and what they think is best.
If you are uncomfortable honestheart then that should be a good sign to talk to your loved one and set some boundaries that you both feel comfortable with... cause really whether they knew it or not, they got away with cheating.... kind of soft cheating perhaps, but cheating nonetheless.
I have a story here and that is that on new years I kissed someone I really liked at the party I was at. I was with Mono and Nerdist and our close friends and assumed (under the influence of alcohol) that they would be fine because she was female. Well, it turned out that my assumption was incorrect, briefly.... they were both surprised and had to kind of regroup in their thinking and came to the consensus that we needed to talk about it.
We did and established that they would prefer that if I felt like kissing girls I wasn't previously involve with then I should take them out of the public's eye and smooch them elsewhere. They would just feel better if they knew I was doing that and that I wasn't getting it on in public. I agreed to that and it was all good. It took some talk and some on the spot sorting out, but we got on the same wave length and re-connected as a result...