I think it must be hard to still work at the same place with someone you had a history with. I do not know if I could do it. I dated a guy I worked with one time and we broke up. Seeing him around the office sucked. Thank god I got a new job shortly after that. You seemed to have handled it well. I guess this is another step in your recovery. Handling social situations with your X.
Stay or Leave the BBQ? I suppose you could treat it like any other social situation and if your not having that great of a time, take an early exit. Say
I had a great time, see you at the office.