I meet with my ex once every few months. We usually just go to lunch. this has tapered off a bit though. My girlfriend knows about this. Ive never done anything beyond talking (and eating lunch)... There is no reason I should shun her. If I was going to get back together with my ex, I would have done so a long time ago.
I'm done with being jealous and worrying all the time. If my girlfriend wants to meet with an old fling and she tells me there is nothing between them, them I'm good with that. yeah, I would be hurt if I find out later that she lied to me, but why worry about something that probably won't happen?