Hi there. All the questions you're asking are good ones, and necessary. If I were you I would not consider getting involved unless you knew for sure that he had talked about it with his wife and she is on board with it. To do otherwise would just make you a mistress of a man who is cheating and lying, a role I am sure you would not want to be in. So, ask to speak with her. Get together with both of them and find out how they envision this working. See if their vision meshes with yours. Ask yourself both what you would want and what you would not accept in a situation like this. Know that you will all probably revisit and revise your list of "wants/needs/will not have" periodically as things progress.
If you do get confirmation that this would be consensual, and you understand fully what everyone is looking for, then I would also hold off on moving in right away. Just because you know for sure you love him and he loves you, and even with his wife's consent, doesn't mean it will work well for you to live with them. Important issues like how much privacy you would have, or sharing finances, are difficult enough to hash out, never mind doing that while starting a romance with someone who has a spouse at the same time! You may want to remain independent and live on your own while in the relationship, not sharing a home with him or both of them, and perhaps have additional lovers yourself. And that is another question to ask him -- how would he feel about your having other relationships, or does he only want a "One Penis Policy" (which most poly folks would deem unfair)? I think it would be smart to be cautious and take the time to develop this relationship on its own and see how things evolve before changing everything about your life so radically at once.
These are the things that hit me right away from reading your post. Good luck and welcome to the forum!
Last edited by nycindie; 09-18-2011 at 11:33 PM.