Personally, I feel it's in my nature to love deeply multiple people. Just as it is in my nature to be bisexual. However, I can choose to act (at least in the physical sense as I have no control over the depth of emotion) on these feelings. I can choose to be monogomous. I can choose to cheat. Or I can choose to form poly relationships. Currently, I choose not to choose. I'm not looking for a relationship with a woman, but I'm open to one. As far as a relationship with a man, maybe I will one day love another man deeply as I love my husband. But, because of agreed upon rules of conduct between me and N, I will not act on this physically.
Nature or nurture don't really matter in my eyes so long as poly is practiced ethically and openly with those involved. Does it matter what drives us to this life so long as we and those involved with us are happy in it?
I'd rather be hated for who I am than loved for who I am not.