Hello, thank for joining me. Please forgive any typos as I get very immersed in my work with you and sometimes my brain goes faster than my fingers.
It is definitely a difficult situation as they have their son in common. Has this happened before where they have spent time together like this or just on this birthday? I would suggest that you sit down with your husband and discuss your feelings about it. I hear that he is defensive. was their an option for you to attend the dinner as well and would that be something you would have wanted?
I am here and awaiting your reply so I can be of further support to you.