I don't blame you for feeling bitchy! What a horrible experience to have to go through.
Unfortunately it is very common in the poly world. You get people who know the theory back to front, have all the right jargon down and say all the right things, but then can't do it when it comes to actually living it.
...and you get those who use poly as a crutch, believing that adding someone else can make up for some perceived lack in their relationship. It rarely works, and often becomes manipulative. Rules are laid out with no rhyme or reason, and the wishes, feelings and priorities of the "new person" are ridden over rough-shod.
In my opinion it's inexcusable, and I wish I could say that these were exceptions, but they're not, and it means that people entering a poly relationship have to be very very careful, looking for the so-called "red flags". There are a couple of threads on that topic on this forum about it.
I do hope that your nasty first experience hasn't soured you completely to polyamory, but that instead it just showed you more of what you don't want in a non-monogamous relationship.
"Listen, or your tongue will make you deaf." - Native American Proverb