If you have agreed that the rules of your relationship are that you tell each other about and you break those, then that is cheating on your relationship, no question.
You ask about support systems - what sort of support do you feel you need? Maybe if you could give us some idea we could point you in a better direction.
Please check out The Birdcage - an open, friendly Polyamory forum for all parts of New York State
"Listen, or your tongue will make you deaf." - Native American Proverb