I've been poly for over 10 years and it's been the best thing for both my life and my relationship with my husband. We were happy when we opened up and now we're even happier because we've learned about how to communicate on a higher level, ask for what we want and need, and view each other as an individual that we are deeply connected to rather than as a co-dependent.

I'm sorry that you seem to have had a bad experience with someone who pretended they were poly but wasn't actually - but that isn't an issue with the relationship style. A lot of people do monogamy badly too - just look at the divorce rate. As was recommended in the OP, this couple needs to do some reading and research and ask themselves a lot of serious questions about what they really want and need and go from there. If more people did that - in any sort of relationship, there'd be a lot less heartache.