There's a nifty web based poly drama that I'd like to turn you onto: http://www.3dogpictures.com/ The episodes are posted to YouTube and are totally free to watch.
The most recent segment was surrounding a dating partner of the main female character who is faux poly. He _says_ he's open with his wife and going to introduce them, but the reality is different. My first impression was that it wouldn't happen to me, since I generally require meeting any additional connected people before taking things to a intense level, but the reality is that almost all of us have been taken in at some point by something that is fuzzy in it's truthfulness.
There was a relationship that I was in several years ago where the woman said she was poly, largely because she figured out pretty quickly that I wouldn't date her if she was monogamous. It wasn't that she was concealing another relationship from me, but rather concealing the underlying expectation that if she loved me enough, I would come around to being exclusive with her, at least with women. This unspoken pressure to change each other into a different orientation lead to the dissolution of the relationship.
I was with a partner for 6 years who was married but cheating, somewhat like the character in the show. Although his wife knew about me, she didn't want to KNOW about the relationship. When I had started dating him, I was totally new to open relationships, so this rationalization worked for me. As I learned more about ethical non-monogamy and polyamory, the "don't ask, don't tell" stopped working for me, and I needed to leave the relationship.
There are so many little ways to tweak with the ethics surrounding polyamorous relationships that learning all the permutations can take time, and most of all, experience to learn. If you're really lucky, you learn by reading source materials on poly, or have experienced people that you take advice from. Some of the subtleties only become clear in the trenches, when you've already stepped on the mine and you're going to have something blown off any way you slice it.
Still, it's worth your time to do the research, talk to others, and continue to refine your own perspective to determine what ethical non-monogamous relationships look like _to you_. With all the different styles of polyamory, defining your personal style, boundaries, rules, deal-breakers, and preferences is hugely important.
Being able to communicate those concepts to prospective partners is a vital skill to cultivate, since knowing something in your head and heart, but not being able to share it with others, makes that information pretty much moot.
So we plow forward, making mistakes and good calls, correcting our course as we go. Don't be afraid to make mistakes. Be afraid of getting locked into poor decisions, or not realizing that something that seemed a good call at the time might not stay that way in perpetuity.