Hold on.. you are meeting her parents WITH her THERE?
Get more info on OM from these people.. find out others who have had this problem with him.. you may hve more support than you think...
If he's done thisto a few other men's wives you may want to gather those married men together and all of you have a "chat" with him...
I would love to help out with such a chat, local or remote depending on how much it would cost me. These things would need to be planned out. I'm sure many of us feel the same way.
Also it would make sense for db'ers to communicate who are in physical proximity to one another. Not to complain and bring each other down, but for support and to make sure each one is enjoying life sufficiently. Plus another db'er would be more than happy to provide intel if he/she had the means to do so.