I put a stop to H bringing my girls around OW (has kids the exact same age), however with your situation, it might push W farther away. H used excuse "They are friends" (meaning the kids), but I said it was his fault for ruining that, and besides they are young, they will have new friends in 5 minutes.
And yes, I got to hear (unprompted by the way) all about OW and H's adventures with the kids. Used to make me physically ill. One day, I was driving the girls to go swimming (by myself) and they went on and on about their week. H and OW had seen each other with the kids every day. I had to throw up at the pool before I could function. Not a good place to be in, I feel your pain.
I think you detaching, not asking where she is, not caring (or appearing that way), but being friendly is your option here. I repeat to myself "Not my mess" and it helps.
