<human>: Can you give me a shortened version of the text?

I won't get too into the backstory. Basically we dated for five years, almost got engaged, no one was at fault for the breakup (enacted by him) but it was nevertheless a rough one. We've been separated for almost two years and don't see each other anymore. 

I've moved on and am in love with my current SO, but Ex still makes me feel very uncomfortable. In the few instances where we do have to see each other or where my friends converse with him, he spends a lot of time trying to find reasons to look down on me (picks apart things like my job, my partner, my relationship, my outfit looking for something to criticize). I think maybe this is because if he can convince himself that I'm trash, it'll make him feel better that the relationship failed? That is my guess but I wouldn't want to claim any expertise on this dude's mindset. 

Anyway, I can't get out of interacting with this guy tomorrow, but I'm so nervous. I just want to be myself and enjoy what I can of the evening, but I don't know how I'm going to act normal around him when I know he will do this. I think I'm either going to be intimidated into silence or provoked into speaking out and appearing the Flustered Bitch. Does anyone have any words of advice? Oh, my current SO will also be there with me.
<bot>: Have no way of avoiding social function/dinner with my ex tomorrow night, need advice on how to keep cool and not freak