But OP doesn't even KNOW that Mom hasn't! (Aside from the fact that it is NONE of OP's business - she is not a party to the order, she is not the child's parent. She IS a legal stranger who needs to butt out.)
I have several close friends who are of the opposite gender - none of whom I'm " engaged in a relationship of romantic, personal, or sexual nature" with. We're friends. And sometimes, since a few of them live out of state, they will come to visit and *gasp* stay overnight. In my house. In a bed. In a bedroom. SOMETIMES, even in MY bedroom (and I sleep on the sofa with the hounds). HORRORS! My KIDS are even home! Sleeping in their own rooms or camping out with me. Yeah - there's a strange car in my driveway. And nothing at all is going on except some friends are getting together to chew the fat. *WOW* That's really radical. I'd love for the kids' other parent to make something of THAT.
Seriously, OP - get a life. You sorely need one.