She's mentioned that she's going to bring OM to her family X-mas party? Haha - THAT sounds like someone who has just recently started an affair. Tuck that away and see what happens in Dec. As my IC says - don't throw everything into the kitchen sink yet.
W is 5'7" and 120 and trying to lose weight? YIKES. That sounds a little destructive. I wouldn't talk to her about it if I were you, but scary...
I think it's great that she invited you along to the birthday party. Do you want to go? Would it be a 180 if you didn't go? What if you had something else to do that day? I'm not saying you change your plans if you've already told her that you're coming, but that's an option.
Don't worry about the cold shoulder. Ride the waves. Detach.
