Lying is not part of poly. If he's cheating then it isn't poly. If you want it to be then he will need to be honest, communicate openly, and you will need concent. That's my belief anyway.
What do you get out of this? Are you interested in others? I think I would add that to your convo that even if there is no one in mind for you right now, what's good for the goose is good for the gander. It might mean that you go about doing other things in life, not just getting another partner, the point is that it be and even deal in whatever way works for you both.
Anyone want to be friends on Facebook?
Send me your name via PM