I don't frequently meet up with my ex's, but have caught up with them for lunch or other things from time to time. I don't really have any sort of emotional reaction to those - the relationship is over, I've got no desire to get back together with them, etc. And it's easy for me, because I know and accept that who we are now wouldn't work out, and that's why we broke up.
But memories don't always have that same perspective. They're a crystallized point in time, and maybe that point in time is before whatever happened or changed that resulted in the relationship not working out. To me those "ghosts" can be significantly tougher to deal with than interacting with the person in present day. Making more memories in those places doesn't make me forget, but it does help redefine it as just another memory in a long list of them. It gives me options of other things to remember.
What has at least a reasonable chance of working in similar situation - come to peace with whatever happened and simply move on. It doesn't matter anymore. Don't cover bad memories with new shiny ones and pretend those old ones aren't there - of course they are, till your last breath they will be.
It really doesn't matter who did what and who hurt who once things are over, it's over. Process things, expose yourself to them (at least for me it works, weird as it may sounds smoking weed and mulling things over and over makes them closed quite effectively in relatively short time - but that's my own unique mindset, no clue why it works like that). They are your emotions after all, part of you. No point trying to act differently.
How to know you really processed them? For example meeting your ex won't trigger any stupid emotional reaction. Imagine granny meeting grandpa when they are 80, would they still hold grudges? What would be the point?