It seems most straightforward to just say that if there is another man there, you would feel uncomfortable/sad/angry/etc, and whether you need to be concerned. I know having another guy present when I see my kids would make it very difficult - an invasion of my sphere - and I would not accept it.
Good luck -
Luke
M58, xW54 S22, D18 M 1984, D 2016 Living a new life.
