I once heard advice given to a group of salesman, and it went like this:
"Go make your peace with God, then come come talk to me. Stop trying to convince people, and you will sell them every time."
It doesn't sound like your friendship with Buddy is quite right to "introduce" him to "polyamory". It doesn't sound like he's ready for the jargon, frankly.
Yes, Love is the answer, I agree, but there are many paths to what we all call polyamory. It sounds like Buddy's perspective might be effecting other areas of his life as well, not just the romantic ones. My advice, in short, is this:
Live your life where others can see it, feel it, and know its honesty. Don't spend your time trying to convince somebody else that your way is the right way, even if it is. When people think that you're trying to convince them, they often become threatened and run to their safe, known ideals.
Be patient with Buddy. Be his friend. Talk about life, love, and spirituality in ways that don't threaten his Christian faith.