I think polyamory is okay, while not a personal preference, I respect that we have personal freedom and choice over our own lives. Monogamy and relationships are social constructs with rules that we just made up but it's not going to work for everyone. Just as in monogamous relationships, in polyamorous relationships every person needs to be full aware of the situation and voluntarily participate in it. Don't worry that she may do things behind your back because polyamory and cheating are two very different things that don't coincide. If this is bothering you and not just a curious question, you should talk to her about it, wouldn't hurt to talk about it even if it doesn't bother you. Communication is very important in relationships. Be honest about how you feel on the subject, don't let us make you feel like you have to like polyamory either, you're entitled to your own opinion, but try not to be judgmental.