I am a Christian, who is poly. Catholics think everything will send you to hell, so I have faced many internal battles on my journey. At one point, I cut all religion and God out of my life. I am finding my way back, but I am doing things differently. I do not know of any scriptures that outright support it. I am sure there are some. If you do a search on Google, you might find some. I have often felt the bible was up for interpretation.
As far as convincing your husband, I would probably leave that alone. Invite him to explore the concept, learn about it, ask questions, discuss feelings regarding it, but at the end of the day, it is something that he will have to decide.
Ry - Me. Panromantic demisexual with a history of polyamorist tendencies. Married to...
Mr. Grey - The once distant stranger that I complement beautifully. DH of 12 years and father of our (3) children.