Cinders, I posted on MrsH thread that I thought her husband's spewing and being unpleasant was a sign that he wasn't happy. Now the opposite doesn't mean that your h is happy. As RCR posted they handle it differently, depending in part of persoality type.
In fact, from what you have posted, you h sounds unusually immature and subject to flattery. That is why he has gone for the type he has - young sweet and adoring. I suspect also that he is somewhat narcissistic, again, please accept that this is very much MO. He is validated by admiration, and may feel less guilt than many of them. He seems truly to feel somewhat entitled to what he is doing. Hence, is less conflicted. They all feel entitled, but most seem to feel more guilt, expressed as anger towards their closest ones, and those who criticise them.
The OW is adoring, and sounds less overtly messed up than some of the OWs. -Although my own view that anyone who messes around with a married man considerably older than herself and with kids, and a wife, has SOME problems!
Perhaps a more likely secenario here is what occurred the other evening - he saw his old life, and missed it. But another scenario is that you will tire of his selfishness and immaturity unless he decides to do some serious growing up.