Hey, welcome. I'm sorry that you're in such a stressful situation.
That moment when you cross over from reading about poly to practicing it is a wild moment, even in the best of circumstances. When it goes the way yours did, I just want to hug you. (((Nelara)))
If I were in your shoes, I'd do a few things. You don't have to do any of them, of course, but if it helps...
My first step, for practicality and peace of mind, would be to demand
an STD test from your husband in a few months (because it takes that long for some STDs to show up), and to only have protected sex with him until results came back clean (or the STD that shows up has been treated and you feel comfortable renewing unprotected sex).
I'd also talk with your husband about closing the relationship (no outside sexual/romantic connections) for at least a few months while you sort yourselves out. This would include not allowing the woman you mentioned to move in, regardless of her living situation difficulties. In your shoes, I would insist firmly
on both points.
From there, there's two separate relationships that need working on: yours with your husband, and the future potential for poly connections (possibly including this woman, if you all agree on it later).
I honestly don't know how to advise working on your relationship with your husband. If either of my life partners had outside unprotected sex while ignoring me and my concerns, I'd consider it grounds for ending the relationship... BUT I can't advise you to leave or stay, because I'm not there and I don't know either of you. That's something you have to work out for yourself.
If/when you get to the point where you want to talk about poly again, I'd recommend figuring out what you envision poly being for you. You can freewrite, or use a tool like LR's lists, above, or the list of potential poly agreements in The Ethical Slut
(pages 154-155, revised edition), or this relationship disclosure form:
Make your husband do it too, and compare what you've written. Find where you're on the same page, and where you're not. Remind him of the poly adage to go at the pace of the slowest member, and don't be afraid to ask him to slow down if you're feeling overwhelmed.
Once you've gotten out of the first steps, if
you're comfortable with it you might want to spend time with the woman-- but not sexually! Go out for coffee, and get to know each other.
No matter what, you are so brave for sharing on here. Thank you for it. Keep posting-- we're here for you.