Look, your porn addiction wasn't ideal. But your W "choosing" to accept another mans advances was a "choice". It was hers. SHE made that choice again and again. It's so easy to blame others. Or put it in a different light. i.e.:
a) Show me a man that tells you he never masturbated (or a woman) and I will show you a liar. You are a human.
b) If your W was putting out in the way you wanted it you might not have spent so much time gratifying yourself!
See what I mean. This is all just frustration at not being in control and loved. She vents to MIL, she vents back - for different reasons. W is feeling unloved by OM and feels you ruined it, MIL is upset that her D is upset (again) and you feel upset that your W had an A now everyone seems against you.
Let the dust settle. Yes, a D might take place, but in fairness I bet there are plenty of people on her that have experienced worse and have got through it (I am not saying a high percentage - but its all possible).
Stop the negative self talk, do some positive self talk. You get what you wish for.
Surfer.
M46/W40/D8/S6/T20/M12/Separated 6/2016,W takes kids Issues2009 Wpartying w/g.f's2013on EA2013PAdeniedWleavesMBR ImeetAP/EAhalts VariousBDDates MFCourse WSpew EAresumes I halt Wrages DBIng4/2016