Personally I don't think you should explore outside of your marriage. There seems plenty inside of it to keep you busy. There are so many challenges in a poly/mono relationship that I don't think it's fair or equitable to ask your husband to go there if you are't able to release him to do the same, whether he wants to at this point or not.
This is only my opinion and there are plenty of poly relationships where the poly party openly admits they couldn't accept their partner being open. It just wouldn't work for me, at all.