You don’t have to meet the OW if you don’t want to.
I split from my ex in 2012. He got together with someone else almost immediately. Our ds goes to stay with him fairly regularly but that has never meant I need to meet the new woman. I am aware of their history and have no desire to meet her.
Neither ex not me make a fuss about it. his life now is none of my business. We leave it at that.