Should i bring it up or leave it alone?

Hey guys. With the help of my last discussion me and my fiancé decided to go ahead with Pre-Marital counseling and it was great. However it also pushed us to want to be more open about things that bother us. One thing that bothers me is my fiancés relationship with his sons mother. She is his bestfriend. While it’s great that they co parent it’s also stressful. They were never married but his loves her other kids like they are his own as well although they are not. He invites his sons mother and her family (kids , sister, aunts , uncles etc) to everything we have weather it’s a cookout, family vacation, his birthday party etc. I’m not the jealous type but at times it feels like he comes with a wife and kids already. Even if she does something at annoys him he will become annoyed with me as well. She has a very huge impact on him. I have 1 child and she is from a previous relationship so I understand but it’s too much at times. This would be a touchy topic for him as he sees them as his family. He lost his parents and grandparents at a very young age so he had really no one until he met her and they were together for 9 years. She’s a nice person but I’m not sure how to go about this. Should I leave it alone or speak on it?