Xeromag's polyamory FAQ
is good for explaining poly basics to partners (and ex-wives!). If you're looking for something more in-depth, Mono has mentioned Polyamory: The New Love Without Limits
in the Book Recommendations
Side note: there a forum protocol about embedding links like this?
You may be betraying part of yourself if you try to live a mono relationship; he may be if trying poly. Its hard to know.
Good luck with whatever you decide to do!