My ex and I met when we were teenagers. We had that old familiarity of growing up in the same place, having the same friends, all of that. I loved his family. His mother was a strong woman. I felt a very strong connection with his siblings. And when his sisters had kids, I was "Aunt Mia," of course. 

We split up in part because I went through a very difficult period after my father died. A few people in my dysfunctional family became vicious after that and I fell into a very deep depression. My ex and I did not handle it well. His mom was helpful and supportive. But it felt like we fell into a hole that we couldn't get out of. 
We didn't have a "bad divorce" at all. People were giving us advice about belongings, money, and attorneys. We were rolling our eyes. We were not out to get each other. 

One of the things I knew I needed to do was also to separate from his family. I did that not because I wanted to but because I didn't want to be that hovering ghost of an ex "marking territory." I wanted to make sure he had the space he needed to move on. 

A few years later, the ex and I reconnected as friends. Not BFFs by any means, but as people who communicate maybe once or twice a year. Family updates. That kind of thing. DH has met him. They get along well. We have good boundaries. 

I have said for years that the thing I missed most about splitting up with him was his family, because they were my family, too. They were actually more family to me than my own family was. Especially being in this situation with skids who have hated me just for being in this position of being their father's wife, I have so much missed the big Christmases, the talks, the sense of family. Of being Aunt Mia. The situations are like night and day. 

I have some of that in my own family, but through the years that has dwindled because of some dysfunction as well as geographical distance. 

I guess this is why I feel so strongly about BMs not intruding into their ex's lives. When we decide to divorce, a lot of territory comes with that. But losing my ex's family was one of the biggest losses of my life. Sadly, they were part of the deal.