If you have not researched the topic of boundaries, then that needs to come before you start throwing that term around loosely. Sometimes a newcomer gets in a big hurry to apply something without fully understanding how it works.
A boundary is to protect you, your son, and your personal property. It is not a method of controlling another person. You first have to realize just what you do have control over. That is an easy answer. The only one you can control in this stitch is JAS. Of course you have say over your child, however, if she moves out of your house.....she is free to introduce anyone she wishes to meet your son. You have no control over it. Unless you can show proof he is in danger, I think the law will stand behind her. Come to terms with what you cannot control.
I am a strong supporter of enforcing boundaries, and believe me, if you set it.......you better be prepared to carry through with knowing how you will enforce it. Do you know the difference between a boundary and an ultimatum?
A lot of guys start crowing about their boundaries to their WW's, and just get rediculous about it. Their true intent is about controlling her, and it proves to be useless.
Take time to think about your core values, Jas. Know what it is that you must have in your personal life. What is it you can't live without, based on your core values? What are the things you will not tolerate? Then, realize that whenever your boundary is dishonored, you are the one to make the next move.
I see dozens of newcomer H's tell their WW they won't live in an open M. Okay, that's fine. But when she makes no attempt to honor that boundary he's set.........then what? So, be sure you know what you are doing.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!