I haven't seen anyone here who was "left in the dust" because of an OW or OM. The OW and OM made it into the M BECAUSE of the problems in the M, they didn't cause them.
If you really want to continue your Rs with your EX-in-laws, then you have to be a friend to their family. This means NOT wanting XH to have a bad life, NOT wanting him to be in pain, NOT continuing to condemn and judge his current life. As long as you are against XH in the present, then you are no friend to his family. This is why a friendship with you would be taking sides BECAUSE you are opposed to XH. If you aren't opposed to him, if you are detached, if you make his life irrelevant to yours, then his family won't have to take sides by being friends with you, anymore than they'd be taking sides by being friends with me. It is YOUR opposition, your continuing insistence to making your life about XH, that leaves no space for them to be friends with you.
They could deal with: "I think XH should have done things differently when he left our M. Still I wish him well now, though I really prefer not to talk about him at all. I try to mind my own business, ya know?"
They can't deal with: "I think XH should have done things differently when he left our M. He should pay for what he's done. You should hate him and his trollop that ruined my M. They don't deserve to be together, they don't deserve happiness. I wish them both the worst. My misery is their fault. Now, shall we have lunch?"
[yes, i'm sure you would never say such things, but let me assure you that you still communicate that message loud and clear]
As for not having any extended family, I think you said your dad was one of 12 siblings. No doubt you have a ton of extended family. You already found one cousin. Why don't you make finding a dozen relatives your 12 days of Christmas? You could even do an advent calendar. This would be a positive and exciting place to put your energy and start building your OWN support network so that you don't have to rely on one that is designed mainly to support your XH.
