You can try it, but you have to think about this...how is she going to react to your suggestion? Will she take it out on your son for telling you about the OM coming by?
How about saying something like this "wife, I want you to know that I am more then happy to pick up son and have him spend the night if you should have plans when he's w/you. Sometimes the little man gets confused when you have guests and doesn't understand what is going on."
Of course, you can change this any way you like. But, my concern is will she take it out on him for telling you about the om staying over.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.