There does seem to be some confusion here. It sounds like you have agreed to lots already, so what has made him think that you will renege on your initial agreement? Have said that you will do something in the past and then changed your mind? I can't help but think his anxiety about your not following through is related to some other issue.
Great idea to make sure you both are in agreement about what is meant by open, swinging, poly; every new word should be clarified I think, just so you are on the same page.
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