Thanks for all the good advice, LH Steve Gigi, much appreciated!
I ended up not saying anything at all.

Just came home after a few days with my parents and New Years with my brother.
Apparently XW and D3 went and met OM today.
I left the room as soon as I heard and later told W I dont want to talk to her right now. Im furious atm.
Will go for a walk. Talk to her tonight.

Me: 34
Stbxw: 30
D:5 D:3
Mini bd: May/June 2019
Married: Aug 2019
BD: 6th Dec 2019
OM Confirmed: Feb 2020
March 2020: I filed for D
Waiting for D to be finalized and W to move out end of January 2021