SA - I am so sorry. They have an empathy and sensitivity bypass/filter specially fitted I think.
B is right about reaping what they sow, and I am truly not gloating about this one. I feel desperately sorry for both my xh and my children that they have largely factored him out of their lives. I have encouraged all attempts on both sides at rapprochement, as advised here. Good advice, but unfortunately, usually leads to further hurt, as the MLCer is unable to follow through on anything.
They may well be seeking their lost youth - but it involves hurting others. The other thing is that your h will probably not remember any of this later on. So a trail of devastation and no recollection of having done it - like an emotional drunk.
Sleeper - it actually isn't the OW's daughter's fault. Just think what a messed up little soul she may be.