I, personally, would just say "hey, this is who I am, take it or leave it."
Possibly you could in a more thought out and less harsh way, but that would be the basic message of it. If you're not happy with only one person, you shouldn't have to stay with only one. Your own happiness is the most important. Those who don't agree with you and your polyamory are free to go find someone else.
[Insert witty comment here]
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