I do feel compassion for what you're going through, but I'm going to be frank. My gut response says you should wait until after your next treatment and see how things go before bringing up anything about poly. Stay focused. I have a sense that it is out of frustration that your mind is going to (possibly fixated on?) this other guy. I would think the more sensible strategy would be to discuss surrogacy or adoption rather than bringing in another guy's sperm. In the midst of all you're managing right now, to talk to hubby about a guy you already know he doesn't like "at all," I think would add unnecessary stress to you both. You've been so patient so far, just stay with it a little longer and set aside poly as an option for now. Besides, if you do become pregnant, having an additional totally new relationship could just be another headache, when you will need to focus on staying well for the pregnancy, childbirth, etc. That's my take on it.
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein