You should definitely do this. It makes no sense to turn this down. If it ruins their marriage, then that's their problem. It doesn't matter that you work with the guy. If he decides to tell all your coworkers, then it would make him look an *** as well for letting you bang his wife. You and him are not that good of friends anyways so it's not like you will be ruining a friendship. Just think, possibly after it is all said and done she will continue to call you, lol.