I'm sorry. This is the worst. I've been there and walked this walk.
I would only maybe 50% believe that OW won't be there tomorrow. Maybe less.
You can and should talk to your lawyer about this because there could be some nuance in your situation that I'm not aware of, but barring that, at the end of the day, unless you can prove that OW is somehow unsafe (i.e., a registered sex offender or something), there is little to nothing you can do about this actually happening.
WH can bring anyone he wants to his home and around his kids. His idiot friends, his shitty neighbor, and his AP. All are fair game, sad as it is.
As you know, WS's can do a lot of truly awful things and it's not even illegal.
What you *can* do is keep a watchful eye on the situation, check in with your kiddo, ask for a daily (or whatever) facetime, etc. Any hint of *anything* that is over a boundary, unsafe, etc., and you can pounce on it as the strong mama bear you are.
In the meantime, you can cultivate an environment in your own home that is always safe, warm, loving, and sweet for your kid. You can support your child at this time because it's really hard for them, too. Very new and awkward and confusing and sad.
You can avoid grilling your kid when they get home, asking them questions, etc. You can avoid any hint of putting him between you and WH, and instead just be the loving and supportive mom you are. If you child wants to tell you something, create the space for that, but otherwise just be supportive.
While your child is gone, you can fold their laundry, make their bed, buy their favorite groceries, maybe get them something special for when they return.
Again, I'm sorry. It's the manifestation of your worst fears in divorce/separation. It does get easier over time, I promise.
[This message edited by Okokok at 2:15 PM, May 16th (Saturday)]