I've been divorced quite a few years but my exh (who left for OW) is really quite nasty and spiteful and goes out of his way to make life as difficult as possible to the point where it's almost unbelievable how horrible he is to me, and he's nice/nasty to the dcs so that they never know if they're coming and going. Most the time I try to let it go over my head (because he'd like nothing more than a fight) but occasionally it feels quite draining.
Most of all though, the behaviour is so vindictive and awful and it's just hard to believe anyone would act like this. I would genuinely have been amazed when we were married if someone told me he would be like this in the future. It's as if he wants to destroy me.