Moth,
I will be dealing with this same thing in my situation a couple weeks from now. W has a horse show about an hour away from where we live. Her dad has a house there that just sits empty so her and a few others that ride will be staying there. The OM in my sitch owns a horse show company and is putting on this show so he will be in town for a couple of weeks as well. As far as I think I'm assuming he is staying at a hotel and not with W.
Having said that, W wants to have son up there from Sunday night-wed.
I am very concerned about this, as I don't want this guy around my son. I understand at some point that if we divorce and move on there will be new people in his life at some point. However, she has been "seeing" this guy since end of January. Way too soon in my eyes to introduce him to my son.

At the end of the day. All I could say to my wife in a calm manner was, "I am not comfortable with S going to stay with you in between shows, but you are his mother and I have to trust that you have his best interest at heart"
She knows my concerns and that's all I can do.
You can't control what she does unfortunately, unless you have a court order saying so.
I understand that this guy will be around and will probably meet my son, but if I find out he is staying at house or doing things with just the two of them I will be extremely disappointed and wil not forget it.

Just stay calm when you bring it up and share your true concerns. This is your concerns for your son, not for you. Remember that


M 37 W 30
S 7
Together 10 years
Married 9 years
BD: 12/12/12(W filed same day)
I moved to apartment 1/11/13
W and S moved to MIL 1/11/13
Peicing: 6/3/13
Reconciled: 7/2013
BD2: 4/20/16
still working on it