I would just like to point out that he is by no means living out MY fantasy...Sorry, could not resist pointing out that piece of apostrophe abuse
Seriously... you do need to consider that he lied once (albeit by omission and that does not make it ok) and he is trying to subvert both of your wishes. How much have you talked about this? I mean, seriously talked about it - all three of you in the same room, no BDSM roles, calm collected environment with lots of frank discussion possibly with a neutral 3rd party present? This may be worthwhile doing - it gives him the chance to say his piece in a less emotional manner, gives you the chance to state your objections and for him to answer them. This way you are no longer at a deadlock - him stating what he wants, you refusing it - there is a chance to move forward in one direction or the other. Whatever the outcome, if done fairly, this will mean everyone is happier because they had a fair chance.