MIL moving out, FIL doesn't know

[AKMD]

That's it really. They have had their problems for years, just not 'clicking' and zero communication, FIL working too hard and neglecting MIL. This year it reached a head, with my MIL being surrounded by 'friends' who keep telling her to leave and talk down FIL (I am completely against this BTW, no one talks down my DH to me more than once). FIL has done his level best to sort things out and spend more time with the family and show MIL how much he appreciates her but it really is too late, she doesn't want to know. They have 5 children, including my DH, another 2 have left home, 2 aged 21 and 17 still at home, MIL told DH yesterday that she has found a place of her own and will be moving out next week, just before Christmas. She hasn't told my FIL and is planning on packing up and leaving while he is at work and the two children still at home are out (she hasn't told them either). This is going to make for an awful Christmas What would you do if you were me?

Why did she tell your DH? If she didn't want anyone to know (eg husband and children at home) then telling your DH, who may have divided loyalties is a strange thing to do. I wonder if on some level she wants your FIL to know.

I had a similar experience some years ago where my brother's partner told me she was leaving him and didn't want him to know. I told her that I would tell him and then she said she wouldn't leave. I did tell him what she had said, he didn't believe me and she left one day without him knowing. It all became very sad but I felt in a dreadful position knowing this was happening and saying nothing