My Ex husband began using 'OW' words and phrases, too.
I was only with my Ex for 7 years, but even in that short time, one knows how they speak and act.
It was like he became a different person entirely.
Swanning around in different clothes, using her phrases, and putting me down at every turn.
It's very exhausting, and hard to believe how much they can change.
Our son is a man now, and he still gets angry over things his dad said.
Your children will know he's being unfair.
They will probably also detest the OW.