I have been reading through some of your situation.
As an outsider reading in I think that if you continue to hold yourself with dignity, and make it look like you can't be bothered getting upset about STBX or OW, you will start to look better and better in exes eyes. It sounds almost like he is going for OW because he wants to rebel. It sounds like she is making you a common enemy to keep him. But don't play the game and be that enemy.
Be above it, look good and dont engage. Take on the attitude that OW is beneath you and not worth your reaction. She is going to just come across as controlling, Disgusting, and selfish. You know why? Because she is. What type of person goes for a married man with 3 small kids? A pretty sleazy one. Sit back and let her dig her own grave. She really can't compete.
You on the other hand have class. Don't waste your time worrying about someone so beneath you. Life is too short. Sure, it's upsetting but you have spent enough time being upset, So go on and get out there and do things for you!
Me: 42 H: 43 Twins age 5 Physically Separated 7/2015
