I, for one, am impressed that you are keeping up such a robust sex life after six years of marriage.  You should be commended.

Given that everything is hunky-dory in the bedroom,

But they sound like they are both dissatisfied.

what harm is it if your husband plays out some online adventures with other women?  You should be feeling secure enough about his desire for you. (he still wants you every single day) that his fantasy life isn't a threat.  But, if he won't role play with you, maybe he'll let you read a few exchanges so you can share in the fun.

By the way, it is very likely that some of the "women" with whom he is communicating are actually men.  You can use that thought for some excellent fantasies of your own.

It does sound like she is looking for a "shallow stallion"