I would have to agree with Mono... although I am probably a little less passionate about it
(love that you are so protective babes!)
It is a bit of a red flag if he won't do some of his own digging on what poly is and has the attitude he has... it sounds like he is not getting his needs met by the whole 1/2 relationship comment and instead of negotiating with you and your husband is being a little boy and demanding he get more.
I know how much time it takes to have more than one relationship! There is no time for anyone to be demanding and childish. If they can't deal with it properly then I would have to agree, it's time to say goodbye and find someone who is respectful to you and your husbands needs and is willing to negotiate. Of course if you put this to him, he may rise to the occasion and change his ways.... especially if you talk about moving on.
It sounds a little bit like he is giving you an ultimatum... him or your husband. Perhaps he hasn't bothered finding out about poly because he thought by now you would want to leave your husband for him...?
Too bad he won't come on here.... Mono has written a lot on this topic and would certainly express his some hard earned wisdom!