Can I get married to another man in a country that permits polygamy?

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I'm getting married to my wonderful fiancé of two years, in September. I'm also polyamorous, and I've been in another committed relationship for almost the same amount of time. I've long wanted to marry the both of them, but obviously polygamy is illegal in the United States. My boyfriend has been looking into ways to get around this, because he wants children but wants to be married first, but so far we haven't found anything useful to us.