Ultimately I decided it was more about being polite, and not slinking away in fear or avoidance. The irony of course is that she snuck the dog back into the house last night and slipped away without me ever knowing she was there. It seems like she hasn't gotten to the same point as me.
When my H comes over to pick up/drop off the kids, I offer him a cup of tea, give him a smile and will chit chat about the kids, weather, whatever has been happening in the news. We do not talk about personal things. This is how I would treat a casual acquaintance who popped over to pick up their child after a play date. Splitting up is not an excuse for poor manners. I sometimes even offer him dinner (if I have made something that can be shared around like pasta).
You are right, the fact that your W sneaked in and back out again shows she has a ways to go before she is detached.
Sounds like you had a great birthday. I had my first birthday party in 20 years recently. I am so very glad I did it. The house was full of laughter and warmth. I have promised myself I will do it every year.
I don't think I need to tell you this, but as long as you stay true to your values, then what your W does or doesn't do can't touch you.
