So... you agreed to stay in the marriage if your husband pursued a relationship with another woman with whom he had an emotional affair and fell in love. I assume you thought long and hard about it, and came to forgive him his transgression, before you consented.
However, while you can't really control what he does with her and how he manages his relationship with her (ie., their commitment ceremony does not need your blessing to take place), you DO NOT need to acknowledge her as a co-wife, or anything other than your metamour (another word for "your significant other's other significant other). Nor do you have to consent to your son meeting her before you are ready for him to, and you certainly don't have to let her move into your home if your husband wants that.
How old is your son? As his parent, if you are not in agreement with something his father wants, you shouldn't let it override your convictions about it. She may be a perfectly lovely woman, but you haven't even met her, and most poly parents will be very protective about whom their children meet and are allowed to be around. You CAN put your foot down if your son is not 18 and making his own decisions.
And while you can't dictate how your husband conducts his other relationship, you CAN ask that he slow things down a bit until you are able to handle such changes. It isn't really about "couple privilege," as some folks might think, but it is about his respecting his wife who was totally blindsided yet still forgave and was willing to move forward into unknown relationship territory. It is called "going at the pace of the one who is struggling the most."
He seems to be going about it all wrong and backwards. I would state to him, in no uncertain terms, that he is to introduce her to you first before introducing her to your son. I would request that you spend time getting to know her before exposing her to your family. As the boy's mother, you have that right.