I don't have any RL friends who have any experience of this, so I'm hoping someone here could give me some pointers.
In July, STBXH announced he'd been seeing another woman, and promptly disappeared to Italy with her for a week. I told him not to come back. We'd moved 6 months before- I'd not been comfortable with this as I had to leave friends, family etc and I was forced into giving up my job- by him. He's now back in our 'home' city with the OW. I'm stuck 30 miles away, looking for full time work, and with 3 kids.
I contacted my in laws via Facebook (no other contact details- STBXH had them) after he disappeared to inform them what was going on. I was very polite and factual about this and told them that as I expected we would be in contact for the rest of our lives due to the children, it was best that they knew what was happening. I received no reply. I still have had no contact, although my STBXH has taken the kids to see them, and the kids have stayed there.
I feel hurt that I was/am going through one of the most difficult periods of my life and they couldn't even reply- even a few words- sorry to hear that but we can't take sides etc would have been fine. We'd split up before because STBXH had been lying/disappearing/verbally abusive on a daily basis, but had got back together to give it another go. Stupid, I know.
I never really understood MIL but was always polite. She had been rather weird in the past. For example, she phoned me up once- late at night the evening before STBXH was due to go back to work after paternity leave for child no 3- to have a massive go at me and detailed things that she done over previous years to annoy me. She did this despite having previously been told that I had severe PND with child 2. After that I never trusted her, mainly as I was completely flabbergasted by her actions, why would someone go out of their way to make things difficult for or annoy someone else?! The way she talks about others I get the impression that I am not unique in being a target for her wrath.
So- what do I do now? I've blocked them on FB because I only have people on there who are genuine friends, and I don't want them nosing about in my life if they can't even talk to me. I don't have any other contact details for them as STBXH refused to write them in the address book when I suggested it many moons ago as he had all the details. I would be very happy to have nothing to do with them ever again, and ignore them for eternity. I'd love to do that with STBXH but unfortunately that's not possible 
Is that realistic? Or should I be trying to keep the lines of communication open somehow? I can't help but worry about what happens when I have to attend some family thing years down the line and they are there…. or whether I'd be justified in excluding them given the choice...
I'm hoping someone with experience might have some words of wisdom...