For me, I always go back to these two passages:
1 Corinth. 6:12
"All things are lawful for me, but not all things are profitable. All things are lawful for me, but I will not be mastered by anything."
"A good tree cannot bear bad fruit, and a bad tree cannot bear good fruit. Every tree that does not bear good fruit is cut down and thrown into the fire. Thus, by their fruit you will recognize them."
Polyamory has given nothing but good fruit in our marriage. It has brought us closer, enhanced our bond and trust, and helped to shelter us from one of the leading causes of divorce (infidelity). If it began to bear bad fruit for us, we would re-think it. But as yet, we have no reason to go back.