As you know, I have been struggling with feelings not unlike yours lately. I have done some searching and am pretty sure that fear is at the heart of my latest round of misery.
I am not saying fear is at the center of yours, just that perhaps there is something underlying all of this. I suggest this for another reason. You seem very bothered by the news of your FIL telling people your M is over. I have been fixated on the fact that H took off his wedding ring. He did this months ago and I have known it for months, and only now it is really bothering me? I know you just learned about your FIL's actions, but I think your reaction is too big for the news (I am not saying you are not entitled to your feelings or that what FIL is doing should not hurt). That's why I think what he did has maybe "hit a nerve" triggering a deeper emotion in you.
If you agree, maybe worth some emotional exploring to find the source and deal with that. I have posted about my discovery on my thread.
