We have been poly for a while. Like any relationship it has ups and downs. The most important thing is good open communications. Keep your husbands feelings close to your heart. If he is truly comfortable with you exploring these new feelings the go slowly. Rushing just increases the risk of someone getting hurt.
As for religious concerns, we see love as a beautiful thing that could never be wrong. There will be others who will not agree with this. You need to first find your peace with this lifestyle change.