July I found out about her beau, by late September we called us done. It took until February for her to move out comfortably. we did custody OK.
The following December, after their 10 day eurotrip/advance honeymoon (it was an expense paid volunteering trip for youth, nice...) they were engaged. Married at the courthouse in June.
Had lunch with her and the kids on the fall, not five months after they started cohabitation as a married couple, and she told me, apropos of nothing, "living together is sure harder than dating." I wanted to scream "YA THINK?"
Less than a year later, she called me for help with DV, she was the worst perp, but it came out that he was controlling and physical as well. I predicted that when she still lived with us.
The kids had been telling me things... enough to almost make me weep. She was the same person. I was neutral, so she confided in me and I helped her through DV based upon what I learned here.
Separation. It was another year before she finally decided to divorce the guy she left me for. Scrubbed her FB of him, including the "you go girl!" Comments from her girl friends.
Still married, but physically separated (backing up a bit here) she asked to come back... by text!

No [way in hell].
From what she and the kids told me, he got it far worse than I did, including being arrested and a TPO against his brother. I actually felt sorry for him. The first year I put on my big boy pants, girded my loins, and tried to coparent with the dude. That went OK.
My point is that it sounds like it is what it is. Validating? Maybe. Angering? Likely.
Focus on you and your kids. She is who she is and you are who you are. Play the long game.