How do you cut ties with family

So months ago I went through a nasty divorce. It was a mutual  agreement. When I left I fell off the face of the earth for a few months and since my x wouldn't talk to me he got my cousin involved to relay divorce info between us and it caused issues between us because she felt I dint appreciate her help(which I did). So we stopped talking for a little because we were too busy being mad at each other.  Me and my cousin have been very close since we were little. I'm 25. I always talked to her about my marital problems and How I wished he would love me as I did him and how he made no efforts. She would always advise me to leave and how I shouldn't get pregnant from him, and my x would always say he dint like her.
Fast forward to now. I got pregnant from my current so. We were beyond excited and I being in a happy and forgiving mood reached out to my cousin and started talking to her again. I asked her that since there would now be a child involved she should stop talking to my x so that we could continue on with the close relationship we have always had. (I understand there were cracks created in our relationship when from the divorce) so she told me i couldn't just turn up out of no where making demands and that I couldn't tell her who to talk to and that she wouldn't stop talking to him. He went over to visit my uncle(her dad) for New Years and she also invited him to go out for her birthday (she invited me too 🙄). I tried to get over it because she reassured me she wouldn't speak about him to me and vise Vera. She said they dint talk much, only snapped (snapchat) occasionally. That she would keep both relationships separate. 
I miscarried a few weeks ago and haven't told anyone. She hasn't txt to ask how my pregnancy is going and it's been over a month I told her I was pregnant. Im out of town (because my so travels for a living and I come with) and said I would call to hang out when I'm back in town but truth is I don't want to considering everything. I'm beyond hurt and betrayed by her not willing to put her family first. I don't understand why she won't stop talking to my x. I don't have anything tying me to him so why does she? I don't want to believe what there is something going on. I honestly don't think so. She has a bf 
I already know we will never be like before and although it hurts to lose her as well as my best friend to all this mess I need advice on how to deal with it. Do I tell her I'm cutting ties with her and why? Do I just avoid her?   
I know this was a long.  But I appreciate any advice. 
Has any of you stop talking to family or someone extremely close to you?  How did you deal with it?