I just wanted to say that you are not alone. I think that we have some things in common. Mostly, that I too am not sure if polyamory is right for me. My wife has recently become involved with a polyamorous man and, at times, I feel like my only choice is to go along with it. I guess I have the option of leaving, but I don't want that and neither does my wife, so I'm back to trying to accept it. Communication helps, as does the support of others. I have not posted here a lot, in fact I've written a very long post, but have not put it out here, as of yet, but reading the posts of others and the support given by the board regulars and moderators has really helped me (thank you Kevin).
Sometimes it is a big help to just write down what you're feeling and do your best to disect it, sharing it with your spouse could be very helpful too, it helps them understand what you're going through and can help shed some light on how you're feeling. Always be honest with yourself as your going through this process, try to get to the heart of what you're feeling and why.
I too grew up in Mormon culture, my family was never very active, but I know the culture and the pressure that can come from family and friends to be "normal" and adhere to the word of wisdom. I would encourage you to do what's right for you and not let the religious believes of others, even loved ones, cloud your judgement as to what's right for you, only you can decide that.
Anyway, hang in there, I hope your story has a happy ending.