I just caught up on your situation - read the entire thread before this.
It sounds like you are doing so many things right, and that you are being very strong. I know how difficult it must be to live in a foreign country in this situation - I moved to a different country to marry H.
Lunch with a huge family sounds like a lot of fun!
I have a couple of suggestions to tweaks - just what struck me while reading your thread, you've got so much good advice otherwise.
1) Make sure that most of your interactions with W are positive if you can manage it. I get that she is wistful when she sees you, that she misses her family - but if she walks away feeling heartbroken and sad, she will only hide in OM's arms to get away from and forget about those feelings. If you want her to look at you and wonder if she made a mistake, she should walk away from any interactions with a happy and light feeling, something she wants to keep thinking about. Or with a question in her heart, or even more longing.
2) About your son's behavior towards her - I don't think you should let him act towards her in a way you would not have allowed him to do if you were still married, or towards another person. It is satisfying to see a child punish the other parent for the hurt you feel, but your goal is to bring up a polite and considerate young man, right? The way he behaves towards her now, you could be on the receiving end of some day. I have seen this happen in so many divorced families.
Best wishes and keep up the great work!
M 16 yrs, WH62, P54 3 adult blended kids EA 11/13, BD1 6/14 PA fall 14, BD2 2/15 Piecing 2015, BD3 12/15 Separated 4/16 WH moved OW in 5/16 Divorced 6/15/17