Hypnosis cannot help you make a decision. From my experience, it just makes you more responsive to the opinions of others. (Which is why, even if a friend was just in trance to help her stop procrastinating or feel less stressed, I wouldn't hold her to any promises made the same day, and I respond to an offer of casal sex with "ask me tomorrow, so I can be sure it really is your choice")
On the other hand, this is a serious choice. Either way, you will probably at some point wonder "What if I'd chosen differently?". Once you have made your choice, I would be happy to help you deal with any remaining doubts you have so that they don't bother you so much in future. But hypnosis (or NLP or any similar art) can only help you accept the choice once you have made it. If I were to 'help' you make the decision, you would be chosing how to live your life based on both your conscience and mine. I don't know of any Judeo-Christian church (even the CoS) which wouldn't call it wrong to discard your God-given free will.
Lissar wrote:For the record, marrying more than one person is illegal, but having more than one sexual partner is not.
That depends on your country/state and religion. Even in many areas where polygamy is not legally recognised (such as Britain), a church can conduct polygamous weddings. In this case, only the first marriage grants legal benefits (such as being recognised for taxation/inheritance), but the law won't do anything to interfere with subsequent marriages.