Hi Defacto, I hope your get together goes well. I think light and friendly is the way to go and I wouldn't let your W know that you are still interested in possible R unless she asks you a direct question to that effect. If she does, you can answer honestly and authentically, knowing you'll be fine either way.
WRT OP - If that ever arises with my H, I plan to say that if I have learned one thing, it is that I don't want to live like that (having a third person involved in ANY way with my partner). That is not how I want my life to be - take it or leave it - if you still want to be in touch with OP, I don't want us to be in touch (apart from essential kid stuff).
Good luck, relax and enjoy xx
T 13 M 7 Me 48 H 46 SS 15 BD 7.14 PA D final 5.16 (H filed)
We receive & we lose, and must try to achieve gratitude & embrace with whole hearts whatever of life that remains after the losses - Dubus