For me, polyamory has always been my nature, though I repressed it and usually ended up cheating anyway. I knew from very young I was capable of multiple loving relationships, just as I knew I was attracted physically and emotionally to other women (also long repressed). It was only through alot of pain, honesty, deconditioning, and support from my husband that I accepted and acted openly on my true feelings.
I don't like the idea of using the term to include purely sexual relationship. I know I focus on the love part and the sex is an expression of that, and only follows that love.
I think for me the only thing that has gotten rid of that fear for the future was time. The longer my husband and I have been together, the deeper our lives entwine, and the more we know eachothers hearts and minds through complete openness, the less I fear we'll ever be apart. Should I/we find a new love, it will probably be the same case.
I'd rather be hated for who I am than loved for who I am not.