I believe most of the mid-lifers have addiction issues. The OW is an addiction, i.e. attention, flattery, sex.....
It is a rare midlifer that does not want to take his ex down with the ship, so yes you are lucky in that respect. That does not minimalize the pain though.
I feel so sorry for you MIL, when she needs her son the most he is no where to be found.
Take Care Trusting
Me: 46 H:44 Together: 25 years Married: 20 years Separated: 11-30-06 Divorced 12-21-07 OW: EA began 2005 PA began end of 2006 3 children,20, 16, 6 ex asked for forgiveness 01/16/11