Glad to hear you'll have support but not too much. You're right, that would totally look desperate. And I think you put way too much thought into these meetings. Yes, you want to be prepared for what might happen. But working yourself up into a tizzy just means you're giving your power away. You're setting yourself up for allowing X and OW/GF to determine your mood by being there/not being there/saying something/not saying anything/etc.
I think the best thing to do would be to show up with just K. Then you can wave to your gf across the room and act as if nothing is bothering you. Because that's the goal--to live your life without any thought about X.
If you love somebody, set them free. http://tinyurl.com/2empx2g