I would maybe suggest reminding your husband about NRE because it really sounds like that is playing a part, how long are you in Europe for?
And for me , my wife has concerns about her shape as well she has put on a few pounds that she doesnt like but she is much more than that to me. And I have told her that.
So I might say let him have his fling, if it's really poly the other woman will know about you, and maybe you should meet her.
It can be quite 'lonely' in a place you are not at home for.
As far as the red light district we did that many years ago, we did not partake in anything there but it was an eye-opener.