It's really a bad idea to include another in your cover story as that will always be a weak link... but tell him as little as possible. The less he knows, the better for both of you.
The more I think on this, the less I think you can allow the wives to meet. You told your wife that both of you went clubbing... so your wife tells his wife that he went clubbing, now he's in trouble & didn't even get to party. So he scrambles to save himself & throws you under the bus.